I don't know about anyone else, but peer pressure as you might experience it in HS is pretty absent in college. From my experience, the usual response, if you're not judgemental about it and just straightforward, to "I don't drink/smoke pot/sleep around" is "cool, more for me." So I wouldn't worry that your daughter is going to turn into Lindsay Lohan II.
As far as girls being rude, they are new and feeling their oats, especially if they pledged what is seen as one of the more prestigious groups. They will get knocked off their self-imposed pedestals in a hurry once a guy they like rejects them in favor of some hot emo-girl GDI.
Seriously, this is so common in the first months of college life it's not even worth a thread. It just shows that glowing recs and a glowing high school record don't tell everything.