Good for Carolyn Bourne. If the idea that a household expects its guests to maintain a certain standard of behaviour comes as a horrible shock to 21st century Britain, then the Goths really are at the gates.
Miss Withers, according to Mrs Bourne, declares what she will and will not eat, says she hasn't had enough, and starts before everyone else.
In any civilised household, you eat what is put in front of you. You wait until everyone else is served before you pick up your knife and fork. If you don't like the food, you say politely that you've had enough, thank you, or that you're not very hungry.
These are not some sort of bonkers, eccentric rules thought up by Mrs Bourne expressly to torture her son's fiancée. They constitute normal, polite behaviour.
You don't expect your in-laws to shell out for some celebtastic wedding. If money is an issue, what's wrong with a modest country wedding – especially if the church is filled with your mother-in-law's gorgeous, scented dianthus?
At the end of her email, Mrs Bourne says: "I pity Freddie" (her stepson). Personally, as the mother of two nearly grown-up children, I pity Carolyn Bourne.