A small figure in black was sitting on the pavement outside the supermarket, hands held out. I passed by. Coming out, laden with free-range chicken, Pouilly Fume and other goods, I tried again to ignore the waif - a tousled boy, aged about 15, I thought - and walked off. Dropping a coin and hastening away had not salved my conscience in the past. This one might be young enough to save. I went back and said: 'Would you like to come and clean my car for me? I'll give you a fiver. I live just down the road.'

I realised that 'he' was a young woman when she got up and accompanied me back to my flat. As we went in to get water and cleaning materials I discovered she was in such a pitiable state that I would have to give her a meal first: you can't work on an empty stomach. I asked her what she would like to eat, whether she was a vegetarian; but she wanted a bath more than anything, so I ran one and told her to use whatever she liked of my skin lotions and shampoos while I set about preparing ham and salad, bread and butter and a cup of tea.

She was such a long time in the bathroom that I became anxious, worried that she may have fallen asleep in the bath. When I tapped on the door she opened it, wrapped in a bath towel, and I saw that she had been washing her threadbare knickers in the bath and was about to put them back on wet.

I gave her some underclothes, a T-shirt and a jersey (not my best). We would put her things in the washing machine and then the drier and she would have them back in an hour or so, when she had had a meal and cleaned the car. She didn't like the jersey I offered her, preferring to put her own back on, as it was. I already had an inkling that she thought I was taking over, but my awareness was dimmed by enthusiasm.

She asked me about the red spots all over her thin shoulders and meagre chest. With a rush of fear I realised she might have a contagious disease, or fleas. What of my son? I suggested the wool might be causing a rash and begged her to let me wash the jumper, but she clung it tenaciously, perhaps as a symbol of her autonomy.

Then she showed me some dreadful scars on her tummy, but I couldn't make out how they had got there, since her English was not very good. She was German. My German was worse than her English. The soles of her feet were so blistered, with tatters of dead skin falling away to reveal red, raw patches, that I wondered how she could walk. I applied Savlon and gave her some clean socks. Her shoes were too small and all broken, so I found some newish trainers which fitted her.

She now said that she felt very tired and would like to go to bed. Sharp intake of breath. I'd no spare room and a dinner engagement meant that I would have to leave her in the flat alone. I could just hear my friends and my son telling me what an ass I was when she disappeared with the hi-fi. But I couldn't throw her out, and said awkwardly: 'I don't know you and I have to go out. Please don't spend the evening on the phone to Germany. I haven't got much money at the moment.' I grinned at her and hoped she would play fair. I left her tucked up in bed, like a little hedgehog in winter.

All was in place when I got back and although I couldn't see her in the darkness I was relieved to hear her snoring lightly. I slept badly.

Over the next few days I found places where she could go for shelter, but she seemed disinclined. I could not fathom how to fill in her social security claim forms, and she didn't have an address. I said she could use mine, at least until her feet were better. We found casual work for her, cleaning in a hotel, where she could live in. But she said they used you disgracefully in such jobs. Well, I wouldn't want such a job either; but I pointed out that she had to start somewhere, and tried to show her how she could start building herself up. But she was impatient with this line of thought - she wanted to be rich and successful right away.

During long conversations over our evening meals (when she turned up) I learnt that she came from a middle-class Lutheran family. Her father had left home when she was still very young and she had become 'difficult'; her mother told her she was just like her father - in other words, just like the man her mother now hated. She felt utterly worthless and, at the same time, to redress the balance, wanted to be lord of the moon and stars and loved unconditionally. Having lost sight of who she was, she could not set herself achievable goals, and so had gone downhill.

She firmly believed she was as wicked as her mother had told her she was. She had taken drugs, been a prostitute; she seemed to think that self-abuse was a just penance. I realised I could not sort her out in a few days, but ended up saying: 'I don't think you're wicked. You are good and dear.' I hugged her, trying to breathe some warmth, some sense of self-worth, into her fragile ribcage. Of course I failed.

One morning at breakfast, she said she was going. She kissed me on the cheek and said that I had been a real mother to her. I gave her a tenner and let her go, wishing her well. She wore her old shoes, having left the trainers neatly beside her bed. I cried when she'd gone - but soon felt mightily relieved.

I think she preferred to beg because money received in that way came with no strings attached. She could not take what I offered because I was trying to make her into what I thought she ought to be - just like her mother had done. Church, state or charitable institutions would be rejected for the same reason.

We try to draw these waifs and strays back into society, to civilise them, but, like hurt animals, they go to ground. John Major may be partly right in saying, as he did recently, that some street people prefer to live as they do. The mistake is to assume that they have any options - what we would call options. In her state of mind, Gisela had none.