hoof great choice of subject! Most of my cohort in history went on to do law conversion courses actually (although for many this was because they reached their final year, hadn't got a clue what they wanted to do, and then the law firms came round at milkround waving training contracts and two more years paid study and walking into a £32k job plus golden handshake, and most went 'ooh yeah that sounds good, two more years of being a student, law it is'
(I always thought this was pretty shitty for the students who actually wanted to do the law, and Oxbridge students snaffled most of the training contracts)
Anyway
Choose your college. As PP said there are posh hooray Henry colleges and fab normal ones. At Oxford I would recommend the 'northern' colleges (so called because they're in the north of the city). Former women's colleges particularly - I was at Somerville and absolutely loved it. St Anne's, Lady Margaret Hall and Keble also great. Jesus a more traditional option but still very normal. At the other end of the spectrum you have Christchurch, Magdalen, Brasenose and Oriel - much more rah, I think I'd have had a very different experience if I'd not completely loved my college community. Those colleges tend to have the higher levels of public school educated students, whereas my college was predominantly comprehensive
As PP have said it is very very self directed study. I wasn't taught, I was pushed and challenged. I had the odd lecture, but with two essays a week my learning time was in the library, preparing for the tutorial. You have to be self motivated because you won't get spoon fed. You basically teach yourself the subject, then the tutorial teaches you to think
That was my experience anyway
I was similar to your DD and yes it will be a shock to not be top of the class any more. I think it's a very reasonable thing to be concerned about from an emotional POV. For me it was the making of me, because it meant I couldn't coast along any more. I really had to bloody work - and that I wasn't going to be the best at everything, and that was OK. I say that, but I seem to remember doing fairly minimal work in my second year and having an absolute blast doing a gazillion extra curricular activities
I feel very privileged to have had an Oxford education, but it's not for everyone and it's far from the be all and end all. I had a fantastic time but doesn't mean I wouldn't have had just a wonderful time anywhere else