If the course isn't for her, then fair enough.
Lots of colleges of varying sizes, though, and you also get to mix with undergraduates from loads of different colleges, increasing the social pool to both those you live with (but doing lots of courses) and those who are doing similar courses to you. You can also get involved with e.g., music, as many different colleges, not just your own.
You can self cater at many of them, particularly in second and third years. Sometimes you pay a small termly charge regardless of how much you eat in college, but often it's not that much. And the food in colleges is often very good value and quite good. It's quite nice to go back for lunch! Good break in the day, and very convenient in many colleges. And you can bring your friends back with you. The formal hall is much less formal than people think - yes you wear a gown on top of your normal clothes, but that's about it; there are only one or two really posh dinners a year. And all of it is optional.
Tourists are a much bigger problem in the vacations than in term times! Bigger problem is moving through crowds of students! And really, students are based on a 'site' with lots of lectures/labs, and their colleges, and tourists don't really go into the lecture sites. Between there and colleges, yes, sometimes. In college, depends which college you are at - old, town centre ones, yes, not so much the lesser known ones further away. But again, there are very restricted areas that tourists can go. Open days would not be a good indication of what it's like, because it's out of term time, and in tourists season!
College tutor is pastoral, which is really useful to have someone unconnected to your course - they help with things like funding and health crises and wanting to change course and whatever else you might need. You also have a director of studies, who is in your area, and then in later years, more specific people related to your subject who supervise you and help with dissertations etc.
Doesn't sounds like she's very open minded about it all, in which case, probably best if she doesn't apply, but if the course was really suitable for her and she was rejecting it for superficial reasons like this, she might think again.
People find in Cambridge what they want to find. If they are assuming it's going to be filled with snobs and that it's all spoiled brats, then they will find people like that (because they are there). If they assume there will be lots of ordinary people who are not snobbish and just really enjoy their subjects and are fascinating and interesting people in their own right, then they will find that (because they are also there). I think it's really a case of confirming your own prejudices! There are so many lovely and passionate people from everywhere, amidst the ones who are snobs and spoon-fed.
I think open days are probably not a great judge, either, because I don't know if those who apply are a good representation of those who actually get in. I've known quite a few snobbish types who apply, thinking they have fantastic grades and backgrounds, but don't get in, whereas the passionate student from an ordinary background goes.
All that said, though, I don't think Oxbridge is the be all and end all. There are lots of courses at other places that are probably better in that specific field, and get ignored because of the public perception that Oxbridge is somehow better, which it isn't necessarily. It is very good in some ways, and suit some types of students very well. But there are lots of equally good ways to get an excellent degree. If she doesn't like the city, then fair enough. No reason to apply, if there are other things she wants to do. But it would be a shame to reject a course that is ideal for her because of reasons that might not be valid.