Op, respectfully, why on earth would you not mention ASD in your op? Surely it's relevant to this scenario?
It's only been three months. Do you really think that she has undergone a complete personality change in that time?
What's happened is that she is probably seen what goes on at uni, been shocked herself and then is trying on this persona temporarily, because she doesn't know who the hell she is yet! She probably got drunk on Christmas day, in a safe place, among people who love her, because she's not stupid and she didn't dare do that at uni!
If her objective was to shock you and rebel and shake off her studious persona, and be a bit competitive with her siblings, then she is succeeding rather well! 😀
Obviously it's a completely different story if you think she is genuinely emotionally vulnerable, is allowing men to take advantage of her without realising the consequences, or she is so anxious and overwhelmed at uni, that she is using alcohol to cope? In which case she needs an urgent referral to student counselling.
Which is it op? Only you will know how her ASD affects her?
Just being shocked and outraged won't help though. You need to see beyond the words and behaviour and find out what's really going on! Take her out for a drive on your own. Do an unrelated errand. Just be together without any expectations or objectives. Stop off for a coffee. Talk to her in a very calm way without any pressure. Don't respond as if you are shocked by anything. Be a safe rock. Fake it if you have to.
Her defensiveness and rudeness is probably just a massive front. Maybe mention how overwhelmed you felt at uni at first. Talk to her seriously but calmly about potential risks and how she can protect herself. But do it from a "we love you too much to see you risk getting hurt because you mean the world to us", even when she is at her most putrid. Be calm and loving and see what happens. Tell her you love her whether she is being a complete whazzock or not. There's no need to be a doormat and accept her rudeness without calmly challenging it, but equally if you have to ignore some of the stupid crass behaviour to get to the nub of what's happening, then so be it.
Good luck