If you aren't ready to pull her out now, I suggest you inform her she has ONE semester to prove that she isn't there just to party. And if the results of the next semester reflect she is continuing to do that, she is done with school until she gets her act together. I would also insist that she obtain gainful employment for the summer, or if she claims she can't find a paying job in this economy that she get a full-time volunteer position. It doesn't sound like she needs to relax after her grueling study schedule.
Boundaries and consequences might at least get her attention. If she isn't an alcoholic, that may be all you need. If she IS an alcoholic, you have a much tougher, longer road ahead of you.