Thanks again for all your input, it's been really helpful. I'll try to address the points I remember:
Edinburgh - I'd seen their policy of RUK admissions being very low - and in fact favouring north of England students over rest of England (we're SW England). Of course if she's absolutely set on Edinburgh, I wouldn't stop her at all, my concern is largely with the chance of her top 3 choices all being rejected (due to factors mentioned above re levelling up, never really knowing if you'll get an offer or not, despite good grades). But of course, logistics do play a part, and the journey to get her up to Scotland (or Durham TBH), plus additional funding for a 4 year course, is somewhat galling as a busy working parent.
Choosing Universities based on looks - she is initially basing her choices on her course - it's not actually offered in that many Universities, and she has discounted some excellent Unis as she doesn't like their course (including several Unis mentioned in this thread such as Nottingham). Of those left in her (quite slimmed down ) list, yes, she wants to be in a beautiful building. Yes, I've told her that even the oldest Unis have had to build 'ugly' concrete blocks to accommodate their growth, but she's overlooking that. I went to Warwick (back in the Middle Ages), so am not personally against how a Uni looks, I chose based on course and league table positions, so honestly, this isn't coming from me! And former classmates and teachers have told her how excellent Warwick (and Exeter) are for Classics, so it's not through lack of knowledge on that front. She's also discounted London Unis due to costs of living, and potentially a more fragmented experience (again, this was her decision, I didn't influence that - she loves London, so perhaps she'll choose to spend some time there when graduated).
She's been to a few open days (inc Durham and Oxford), and we've got Warwick coming up, although by then, she'll have submitted her form. Interesting about adding to her choices after Oxford early application, I'll mention that to her.
I spoke to her Classics teacher last night, he's very supportive of her Oxford application and seems to think she's got quite a good chance. Perhaps I'm just trying to curtail any future feelings of disappointment for her, but I don't want her thinking not getting an offer (or an interview) is because she's rubbish. My concern is she could have rejections from all the places she wants to go, and it could really impact on her teenage fragile self-esteem.
But I'm going to take your advice and take a bit more a step back and let her make her choices - her school is excellent at giving advice, and will be so much more experienced in advising than me, so will encourage and support accordingly.