The two women walked on, but I did not need to hear another word to know that the weekend was not a cosy retreat with a lover or a tricky meeting with stepchildren, but an all-too-typical visit with a daughter-in-law. Immediately I saw 100 failed attempts to make friends. I saw efforts to be nice end in frustration as her son's wife bristled or looked blank. I saw her searching for some safe phrase, knowing she would be judged and found wanting, whatever she did, whatever she said. All this was immediately crystal clear, because I am a daughter-in-law.
My mother-in-law is among the most kind-hearted of women. She does not wish anyone harm. Yet in her presence, as she is asking what she can do to help me prepare the family meal, or admiring an outfit I am wearing because it makes me look thin, or commiserating with me because I have to go out again in awful weather to pick up a kid from swimming, I feel as though I am fighting for air, struggling with some suppression of my soul. Feeling this way without being able to justify it is awful, so I took the psychologist's way out: I decided to study in-law relationships. After six weeks of letter writing and phone calls, I had 20 families willing to talk to me and have me observe family gatherings.
The most common in-law jokes are told by men, music-hall style, about the wife's mother: she constantly interferes (dictating where the couple should go on holidays or which schools the children should attend); she fails to respect the husband's sexuality (barging into the couple's room with an early morning cup of tea); she sows seeds of suspicion in her daughter's mind ("you know what men are, trust your mother"). But it is between women that the in-law battle tends to be strongest. Ruth, 33, is a cheerful and confident barrister, yet when she speaks about her mother- in-law, who is visiting her for a week, she sighs like an irritable adolescent: "I came downstairs this morning in a rush to get to work, and Joyce was bustling around the kitchen. `I've managed to get Piers to eat a good breakfast and he's ready for school now. We just have to sew this button on his jacket.' Normally I'm a reasonable and fair person, but all this cheerful nurturing put me in a foul mood. I feel she's implying how much better she is with the kids than I am. Basically, I feel she's showing off at my expense."
Ruth's mother-in-law Joyce, 59, feels constantly rebuffed in her efforts to get close to her daughter-in-law. She is bemused at how charming and friendly Ruth is with other people, compared with how she is with her: "I see her talking and laughing on the phone, but with me she's a different person. I ask her how her day went and she gives me a sullen one-word answer. She says `fine', but she might as well be saying `terrible - don't talk to me'. I try to bring her in to the conversation, but eventually just give up. In the end I only talk to my son or the children. A conversation with Ruth is forced labour."
The mother/daughter-in-law impasse is a tragedy, dividing women who have much in common and who could benefit from one another's friendship. Why is it a relationship which so easily spoils?
Amy, 27, says that it is the domestic setting of the visits that puts her on edge. In-law visits take place in people's homes and housework is emotionally laden. Who does it well may be a sign of who cares enough. But to someone else, doing housework well is a sign that you have notthing better to do. So sensitive are these issues that a request to help with ironing can be taken as an offence. Amy lost her temper with her mother- in-law when she offered to save her a job by doing the ironing.
"I came home glowing because I'd just landed a juicy account for my firm. I started to fold the laundry and suddenly my mother-in-law is crooning over me about the ironing - a job I hate and never do, because it stinks of the drudgery I'm determined to escape. I exploded: `It's not my job to do the ironing!' My father-in-law looked at me like I was going mad."
The daughter-in-law of today often resists the good-housewife image as she hunts for rewards in the professional field. Yet the ghostly force of female stereotypes continues to haunt. We think the Doris Day spectre (remember her song `A Woman's Touch?') is dead and gone, but it can leer at us through others' eyes. "When my mother-in-law tells me what a `good wife' I am," Maria says, "my heart sinks. I can't make her see why I don't want to be a `good wife' in that sense." At 32, at a demanding phase of her career, Maria feels threatened when the "good wife" image is brought in to her home. "I suddenly feel guilty for coming home at 7.30, not helping with supper, and then I get angry, because why should I feel guilty for putting so much in to my work?" Women of different generations are likely to have different ideas about what a woman is supposed to be. Someone who believes that you should have a dust-free house, a well-kept kitchen, and children who look tidy because you have washed their clothes, will not understand the identity demands of someone who thinks that her career is crucial to who she is, while the domestic side is, to her, just an irritating necessity.
It is easy to understand Meg when she says that she can't find anything to talk about with her son's wife Sarah: "Her work is a closed book, so I ask about the alterations to the house and how the garden is coming along, but she's always too busy to chat. We never have a real conversation." The mother-in-law works hard to establish some common ground, but the new woman does not want to stand on that ground.
Then there are problems as women jostle for status. Sue felt her mother- in-law had a variety of strategies for taking precedence: "She answered the phone when she was visiting and I heard her say, `This is Mrs Caine'. I've been married to her son for two and a half years, but she keeps forgetting I'm the Mrs Caine someone wants when they telephone my home."
And there is that tricky question about who is "mum", with final say over all those things most women - for all the change there has been - still dictate: menus, meal times and children's table manners. Lucy complained that her mother-in-law takes over as "mother" when she visits. "She kept passing around the mint sauce. `Do have some more. Sally, try some. Aren't you eating well! Now let's put the jelly into this jug.' She takes charge of the meal."
Here two women form an age-old triangle, each trying to claim the better half of the man, battling over which female role - wife or mother - is more important. But this is not simply a power struggle. It is a battle between a wife's need to be equal to her man and a mother's need to put her child first. When this joins up with women's still uncertain position in the public and domestic worlds, there is war.
Lisa says that every visit from her mother-in-law sets her husband Paul back at least a year in her battle to make him carry his weight in the home. "Paul asks, `Where's the butter?' and his mother jumps up and puts it in front of him. Within a week, he's back to the old routine: `Where's the knife?' means `Get me the knife'. When he opens the fridge and can't find the olives that are right in front of his nose, his mother thinks he's cute. What she doesn't see is that I'm trying to downshift his expectations for domestic service."
But what about all those 40- and 50-something women who worked hard to create an equal partnership with their husbands and raise their sons to be caring and sharing men? Don't they avoid these problems with a daughter- in-law?
One snag is that while many mothers say that they are keen to raise sons to be new men, good intentions are not always carried through. Pam tells me she expects her son to take turns cleaning the kitchen, without resting for weeks on the laurels of one night's clean sink; but she runs after her son's dropped socks, while she shouts at her daughter to pick up after herself. Lia declares that her son will be raised to be a nurturing father, but when he bounces on the sofa, hurtles in to his sister, and rough-houses with his friends, his aggression seems normal; when her daughter shouts and spits, she takes her to a therapist.
Even when a woman is deliberate and steadfast in enforcing gender equality among her children, her nerve can fail when she's adjudicating between her son and a daughter-in-law. Ari, 49, made sure both her son and daughter did their fair share of housework. "I never let Dan get away with laziness. My heart sank when his girlfriends started cooking him meals, tidying his flat. I was relieved to see how Briony stood up for herself and made demands on him. But I don't see how she can keep up those punishing hours now that Dan is a partner in the firm. I'd like to see her at home more, so he has some time with her."
And Briony tells me, "I love Ari, but I can't depend on her support. She'll always be biased towards Dan's career. If she were my mother, I'd fight back. But fighting a mother-in-law over this is something I can't win. She may be a feminist but she's a mother first. She wants Dan to be happy. And let's face it - he'd be happier if I worked less, and looked after him more.'
Carol, 26, says that her mother-in-law, who is a GP, is generally supportive of women and "on the surface, all for equality at home, but when I told her about this new job offer in Manchester, I couldn't see any of her ideals in action. I was really shocked by the way this supposedly enlightened woman said `Commuting would be difficult. Greg would get so lonely. You have to consider the whole picture. I know it's hard.' I'm really offended by this show of sympathy when she implies that what I want isn't as important as what my husband wants. I thought she was my friend. She thinks she's my friend. But I can't trust her with this stuff".
Mother wants what's best for her son. Doing his fair half of family work is not best for him. A mother-in-law remains focused primarily on the son's interests, and those interests, in our society, involve a good career, and a good career depends on long hours at work, with a supportive and servicing partner at home. The needs and goals of a child's spouse just don't register with a mother the way her own child's needs do. So the friendship that a mother-in-law appears to offer can be poisoned by biases she herself may not acknowledge,
"Things can get worse when children are an issue," Charlotte warns. Tamsin, a retired teacher, said that she hoped her daughter-in-law, Charlotte, who was then an MP candidate, wouldn't be elected because her grandchildren saw little enough of their mother anyway. Tamsin is with the angels intellectually, but as a mother-in-law, her heart is in the Fifties. A woman wants what is best for her grandchildren, and a mother at home is the most simple way - if not necessarily the best and only way - of meeting children's needs. "My own mother is far more conservative," Charlotte says, "but she's also more sympathetic with my goals. So if I want to pull out all the stops, she says, `Go for it', even if she knows it'll be rough on my kids. Tamsin gives me these mixed messages."
As wives, we are hyper-sensitive to throwback messages about our roles in the family because, on what is still the cusp of change, we feel the fragility of our gains. Women are in the workplace for good, but every step out of the kitchen is still an effort. And tolerance of a mother- in-law's ambivalence and inconsistency (some might call it hypocrisy) is difficult when you are under siege. But as we become more secure in these changes, will this precarious relationship improve?
I listen to Jenny, a history professor, describe her son's new wife: she's clever, organised, nice though a little too ambitious. "And she's too old for him. Thirty-six! I worry about the state of her ovaries." As I see my friend's warmth, generosity and intelligence narrow into a mother-in-law's perspective, I fear the problem between mothers- and daughters- in-law will continue its downward slide.
Terri Apter is a social psychologist at Cambridge University