I disagree that the sleep schedule is the major problem here. She’s staying up way too late and then sleeping in way too late. This is not at all uncommon for college kids. Yes, the underlying causes are an issue, but the sleep schedule itself is just a symptom, not a cause. If you try to address the sleep without addressing the other stuff, it won’t do any good.
There are several possible issues here:
One, she may be struggling academically. You really do need to know how her grades are. If she is on academic probation, then you need to find out what that means and what she will have to achieve next year. And then you should sit down with her and figure out what she needs to do to achieve that – whether you can help her find tutoring, or whether she can maybe work with an academic coach over the summer to help her learn to focus better and have better study habits.
Two, her anxiety, now that she’s gone off her meds, may be causing her problems. My D had to go off of Prozac last fall (upon the recommendation of her psychiatrist) and it gave her anxiety spikes and panic attacks as well as a serious increase in depression. She could hardly even attend school, let alone get homework done, for a few weeks. And that was as a result of gradual titrating down – not suddenly going off of it entirely. If that’s what your daughter has done, that may explain everything else right there. You MUST take her to see her psychiatrist and get to the bottom of what’s going on.
Three, even if she is still taking her antidepressants, she may be feeling depressed anyway. College is a big change and a big stressor, and many students, including those with no mental/emotional issues, go off the rails to some extent. Partying with her friends and refusing to make any plans for the summer sounds to me like she may be hiding from the depression and anxiety by refusing to think about it. The problem is that all the problems she’s avoiding will still be there when she goes back to college in the fall.
Here’s what I would do: first, make an appointment with her psych and probably with a therapist as well. Second, figure out where she stands academically so you can plan for next fall. Third, you need to remember what your job is as a parent of a college student. As others have said, she’s 18 and the only way you can put rules on her (curfew, must be asleep by midnight, whatever) is by threatening to quit paying for college if she disobeys. I don’t quite see you doing that, and I’m sure she knows it too. So quit trying to lay down the law and instead tell yourself that your job is simply to help her be successful in life. After all, that’s what you want, right?
She has the summer to do whatever she needs to do to have a successful sophomore year at college. That may mean she doesn’t get a job this summer, but instead focuses on her study habits. It may mean that she spends the summer simply volunteering somewhere where she will enjoy the work and it won’t put a lot of demands on her. (If she’s at an elite school she’s had a demanding year – taking it easy this summer may be what she needs.) Don’t forbid her from going out with friends – instead, tell her that she has to have some kind of regular schedule during the day. If she doesn’t have a job, she has to commit to a volunteering schedule, or to having sessions with an academic coach, or something. Once she has a regular daytime schedule, her sleep schedule should adjust. And once she has a reason to get out of bed every day, hopefully she won’t feel the need to drink or get high every weekend.
Hope this helps.