Lots of good advice here already. The only thing I’ll add is that as long as your D is maintaining good grades (and a 3.9 at a top tier is more than “good” it’s awesome), then I’d encourage her to finish the year unless you are worried about self harm. It’s difficult to see your kid unhappy but at this age I think you also have to resist swooping in to rescue her (again, the exception is if you think she’s going to harm herself). I agree that social media can give a misleading impression that everyone else’s life is perfect. Also I think we (parents, the media and the colleges in their marketing materials) sometimes build up an unrealistic picture of what college life will be like.
My younger D is a freshman in HS. I’ve changed her school twice since 7th grade in response to her stated misery. Guess what, she wants to change again. I’ve been taking her to therapy and part of the therapy is teaching me how to respond when she says: “I hate school, i’m miserable. I have absolutely no friends, I don’t like the people at this school, I don’t like the teachers, I don’t want to go”. I’m supposed to validate (acknowledge) her feelings but without trying to rescue or fix the situation. School starts again on Monday and it’s ratcheting up again. I’m spending a lot of time this weekend saying various versions of: “I know you hate X school. It’s hard to feel sad and lonely.” I don’t try to talk her out of her feelings even when I think they’re irrational. Fingers crossed that she gets off to school okay on Monday morning.