Completely depends on a few things: how much you earn, which university (different cities can be more or less pricy than other cities), how much student loan is she getting, how much savings does she have, do you expect/want her to work in the holidays next summer etc.
My DC both went paying everything themselves in terms of accommodation, tuition fees, living costs, transport, food, nights out. My salary is OK to live a nice life but not huge.. I couldn't support them without it having a huge impact on my living and so didn't. My exH doesn't support them at all. When my DC started they were on the cheaper fees and the payback system for student finance is much more reasonable than now.
DC never had any trouble, they learnt to budget, worked summers, used savings and their student loans only covered most of their accommodation, not all, but they survived and didn't get in any debt. They didn't get holidays paid either.
So one answer is give her nothing/very little and she will be fine, don't be guilt tricked into giving lots if you are tight on money.
But if I was in the position to be able to support them, I would, and I would give about £30-£40 a week if it is just for going out, extra food/toiletries bits (assuming the food you mention in your original post is separate to this money? Food will be about £25-30 a week on top), transport home should she want to visit you and anything else.
How does she currently afford to buy clothes and go out etc?