Her state might be a factor in her believing PR or falling over. But I think what a lot of us are struggling with is why people keep trying to find pathological reasons why she was drunk.
Students, non students, lots of folk of different ages go out to enjoy themselves and occasionally drink too much. It happens, try a&e on a Friday night.
They were going to a club for a student night and decided it was cheaper to drink beforehand. Loads of students do it. It's not a sign of anything.
She should have been safe from PR. It's his behavior we should be pathologising not Libbys. She hasn't done anything wrong.