Hi, my daughter is in her first year at Cambridge. She went to a comprehensive school with relatively few Oxbridge applicants.
A year on, the interview seems the least of the stressful experiences she and we have endured since she applied! She had 2 interviews on the same day, and a brief test. In the end I took her, she was stressed enough without a night away before hand in strange surroundings. Outfit - smart trousers, top and cardigan.
I think the interview was the really important bit, and they seemed most interested in the ability to argue a case, yet be open to someone else's view.
Anyway, she was pooled, then accepted by another college. The worst bit was waiting to see if she would be fished out of the pool. I had been quite laid back till then! Do not underestimate how horrible the waiting is.
Then, she had to get at least AAA. We had no idea whether it would be really difficult to get an A (first year they were used). She worked very hard (with a few rebellions - 'it's too hard, I don't want to go anyway')and had some extra coaching from a teacher at school, but declined all offers of revision cramming courses etc.
The day before results day was pretty awful too! Very nerve wracking! But in the end she exceeded the offer by a long way, and finally admitted she would have been devastated not to get in.
I think she would now say it was worth it- she is happy and thriving. But it was not an easy year at all, and the pressure didn't really let up till results day.
So, I really hope it works out for your DD - it is achievable for an 'ordinary' girl, but you need to be a calming influence for a LOOOONG time!