SilverProteus wrote:
I would just be blunt and tell her that studying for an important exam and college are important to you, and that's something she just needs to understand.
I would go with this. Part of the responsibility is on her to respect her friends doing what's healthy for them and having a life of their own, and there's only so much you can say to make her see that.
That does sound like a difficult one, though. I think that sometimes people who are very lonely place an unfair burden on the one or two friends they have to be their everything. Having so little, they try to get as much as they can out of the people who are in their life which might be more than they're actually capable of providing. If she can find other things to do and other people to talk to, I think that will help.