What a choice ?
Can she go and stay with some of her overworked friends at Oxford and see what the reality is. Turning down Oxford is fine - but she should know what she is turning down, rather than rely on hearsay. And then with some at Bristol or Edinburgh.
My dd is in her first term at Oxford and is finding it hard work, but so far challenging hard work in an an environment she loves where everyone else is working hard as well.
This is (at the moment) totally compensated for by her very supportive college and peers, and by the enormous number of things she is doing on top of work. She is having a brilliant time and couldn't wait to go back this term.
I do see that it isn't this way for everyone. But I just wanted to show that it isn't necessarily all work.
If she has already been to a very academic school and been the sort of girl who does a lot as well as her normal academic work she will probably find the work OK. It is clearly the sort of place where you have to sort out your time management if you want to do a lot.
My dd isn't finding it provincial - and she comes from the Central London. She is instead finding it accessible and fun. In a way the size of the city allows her to do all the things she wants to fit in.
She is only one term in, so I can't comment on her long term happiness, but right now the college system works for her supportively, administratively (gets fed regularly and cheaply!), financially, and socially and the tutorial system keeps a naturally lazy girl who wants to cram everything else in on her toes.
Ask your daughter to not dismiss it out of hand, and to not dismiss it from hearsay, but to go and have a look during term time, and then choose one of the others if she still likes it better. She has time before she has to decide. Choosing between Oxford, Bristol and Edinburgh is incredibly luxurious.
Ask her to look at it all properly. And then support whatever choice she makes, as surely there is no wrong choice with this selection. And then don't look back !