I never went to open days, lived at home to go to a local uni to save money and, if I'm honest, because I was scared. My dad pretty much shrugged at it all, and my mum was desperate for me not to move out, so I didn't.
Even though I ended up with 2 top degrees from was a top 10 RG uni, I definitely missed out on a lot (and STILL wound up with massive debt!). I don't think I really "grew up" until I moved out at the age of 26.
The thing is, University isn't about learning facts about a subject, and in fact every major university tends to be criticised for teaching quality as lecturers are focused on their own research to further their careers and deepen the spectrum of knowledge on the subject. Therefore for the most part you could probably learn the same amount with online syllabi and online free courses, although you wouldn't be accredited I suppose.
University is actually about growing and becoming better at judging and interacting with people; about learning all the practicalities of living alone, and while you CAN do that in later life, it's harder. The big thing that living on campus offers that no others stage of life does is this huge mixing pot of people all ages, all interests, lots of clubs, in a safe space with dedicated set of student support services ready to help with any issues they're able to. (Sadly of course not everyone thrives, but the majority find a place pretty quickly, and unis are getting better on the support provision as the years go on.)
For me, I wasn't a total loner; I had lots of friends at uni and spent weekends watching movies with them or going to parties etc, but with no car, an inevitable early curfew out of respect to everyone else in the family, and several part time jobs, I ended most of my free time at home studying. I never forged deep bonds with anyone, and I regret that a lot as actually when you start jobs and moving around, you never have that network on offer again. There were some other issues in my family - my mum has some mental health issues - but I think it limited my eventual career too as I didn't go on trips, didn't gain many skills from societies, didn't do work experience abroad, and so on.
So, sorry, I'll stop rambling, but ... If I could do it all again I would be going to every open day possible, preferably with two supportive parents to get their grownup advice and opinions! :-) Hope this helps offer you a perspective, and really hope it goes well for her!