you sound as closed minded as she is, and determined to believe that her perceptions are true. With that mindset, you/she will probably find that they are. With a different attitude, you'd probably find a completely different set of people.
Lots of people have said there are plenty of worth alternatives - it's not Oxbridge or nothing. But what they've tried to point out, with the benefit of having experienced it - is that many of her objections don't actually make sense when compared with the reality.
The size of colleges really makes little difference. You socialise with people from many colleges, and many courses. It's quite nice having such varied social groups. Many hobbies are across the whole univeristy, or are duplicated at many colleges, and you can join them too - so you can often find a group at the right level, whether it's sports or music or whatever. And there is a great custom of doing extra curricular things - not pressured, but it's seen as a perfectly normal thing to be doing, involved into whatever societies you choose, however weird or nerdy they might seem.
I think it's actually easier to meet people with a collegiate system. Universities of 10,000 can make you feel overwhelmed and isolated (I had one of them too).
In contrast to that article linked above, I found that most students became very aware of their privelege, and somewhat uncomfortable with it, rather than assuming that they deserved it. Many very much appreciated the extras such as book grants and so on. And many people I know definitely did say that they couldn't afford things like balls, and/or worked their way to a ticket, without anyone batting an eyelid. I also know plenty of people at other universities who also had balls and events and formal dinners - they're just not portrayed the same way in the media all the time.
Focus on the course, and on the nice people doing the course because it's really what they are most interested in over anything else, and that's where you'll find the people that oxbridge is really most suited for.