I remember when I arrived someone described it as:
You've been top of your school all the way up, didn't have to do that much work to be at the top end of the class. You're grade 8 in an instrument, play sports at a county level, you had a strong friendship group and always got the top part in your drama group.
Then you arrive at Oxford and find that your next door neighbour wrote a symphony in their spare time which is being performed next month by the BBC Philharmonic orchestra; your try out for the team in your sport meant you were surrounded by people who were on the national squad, you've got to start from scratch friendship wise and everyone else seems to have met their bosom mate on the first day, and you thought you recognised your subject mate from somewhere and it turns out she's been on TV since she was 6yo and to add to that you're now middle of the road academically. It's a huge shock.
The good news is that most people feel the same - even those that seem totally at ease.
For a start off, the people I knew that really struggled academically the first couple of weeks all settled down and did really well. One went from in his first term thought he'd have to drop out to getting in the top ten first in his (large) subject.
Encourage her to join a few societies and see how she gets on. Sometimes the silly ones can be the best. The friends I've kept up with over the years are all from a society I didn't join until about 3rd or 4th week.
And encourage her to go and talk. I was there over 30 years ago and there was loads of encouragement to speak to welfare - and many people went and had a cry on the shoulder of the welfare people. The chaplain almost certainly is one, but there will be plenty of others. Both my tutors were on the welfare list, although one was pretty taciturn in tutorials I believe that people who went to him with welfare issues found he was good.
And on the subject of tutors - they picked her. They do not want her to fail. So if she's struggling, go to them and ask for help. They're not going to give her the answers, but they will provide help. They won't get angry at her or think she's stupid - they're used to that and they would far rather someone came and asked for help, than struggled on feeling miserable.
The other thing is make sure she's eating at least one meal a day in halls. It's quite daunting going there in a lot of ways, especially when you are feeling new and vulnerable, but you end up meeting other people and chatting, and maybe someone saying "we're going to... come on..." (I went to some very dodgy interesting places through that) or second years telling you how they struggled in the first year etc. I found people didn't always sit with groups of friends as people arrive at different times (if they have formal hall every evening that might be different) so you'll often get chatting to the people near you.
I remember when a couple of the lads decided to "borrow" a dining hall bench... and the time someone fell off the table while carrying their food (believe it or not, we climbed over the table to get to the bench against the wall) and things like that make everyone laugh and join in together.
And matriculation is fun. Out in your sub fusc for the first time, getting tourists asking why you're wearing that. (although even more fun for exams because they don't believe the answer) The fun of all the boys who came with cuff links and don't know how to tie their bow ties and are wandering round asking for help with both. I remember the organ scholar declaring in despair that he was going to start charging for tying bow ties! Seeing the scholars' gowns getting caught on every doorknob and trying to resist using your mortar board as a frisbee. Not recommended. Friend had to buy another when it disappeared over the wall of a private house!
And then you get to promise not to take sheep into the library nor kindle any flames therein. Although maybe they've made that more up to date. Anyway did you know scholars of St John's have the right to graze sheep on St Giles? There's no grass there now, but maybe that's why they have that rule.
There's a good chance that tonight they'll have matriculation formal hall, where they'll probably be sat with their tutors and other subject students. Everyone is still feeling nervous and unsure and formal hall is so far out of most people's experiences, but it's shared and gives an opportunity to meet people.
Plan to go and visit her in 5th week. 5th week blues often hit hard that first term, and it will give her something to look forward to. Or maybe send her some money so she can take a few friendly people up to Little Clarendon Street to find G&Ds ice cream parlour next week. It's worth the walk.