some good further suggestions here OP.
Good to hear saying less about her essay issue seemed helpful.
that's very detail, though. What I was getting at is, how can you step back from being so involved in ALL her decisions, and have others said, empathise with her feelings right now ('sounds like you're having a tough day') and less, or no 'solving'?
So her university choice: whether it was or wasn't a mistake, that's no longer relevant. She is where she is. You ruminating on the mistake is destructive, and I'd bet she can feel your judgement and disapproval, whether you voice it to her or not.
I'm in the camp that nothing is really a mistake. Or rather you learn just as much if not more from the mistakes as the 'right' decisions.
What do you want her to say or do? Would you feel better if she said now you were right, and it's the 'wrong' university? What would that achieve other than your vindication?
If she'd taken your advice, and still broken up with her boyfriend, maybe she would have blamed that on you.
It does come across that you are still trying to manage (even micro manage) her life. Maybe that is contributing to her anxiety?
Would happen if you adopted the mindset of, 'there's no such thing as a mistake, only chances to learn and move forward'?
I spent my 20s pursuing a career in no way related to the (very prestigious) degree I earned from a (very prestigious) institution. It was tough, though I enjoyed some parts of it. I'm sure my parents thought that was a mistake (my dad made it clear he did) in this aspect my mum did better and trying to support where I was. Eventually I moved into something else and now have a much more successful career doing something else. But the experience I gained doing the first thing is still useful to me, in lots and lots of ways.
it sounds like she lacks resilience, but resilience comes from accepting and moving on from mistakes, not always seeking to avoid them, or endless regretting the ones we make.