She's terrified of the physical demands of romantic entanglements.
I just reread this thread and I think this is possibly the explanation for the baggy clothes, the relationship with the girlfriend, and wanting to be around younger kids. She is protecting herself, hiding herself, trying not to be noticed. Not that this is the case, but from what you have alluded to with regards to the older boy, this sounds awfully similar to what victims of sexual abuse do to protect themselves. Again, not saying that she was abused, but you have said that it was a very damaging situation.
Also, she probably is right about most psychologists - she probably does think in a much more complex way than most of them. Which is disheartening when you are crying out for someone to "get" you. Of course, it's also a hallmark of teenagers to feel misunderstood. Is there any adult with whom your daughter feels a mentor-mentee relationship who might be willing to get together with her more just to hang out and talk?
Another thought that might help relieve some of the pressure she may be feeling either about college or college-age relationships: Can you come up with one or two other alternatives to her moving directly from high school to college, that might buy her some time to grow more comfortable with the idea of advancing? Could she apply to colleges with the rest of her classmates but then delay enrollment for a year or two to work or travel or just unschool? I know that comes with other issues (math progression being one that immediately enters my mind), but maybe just the idea that she has options will release a bit of the pressure she may be feeling (but still encourage her to do well on the SAT and in school so she does have options).
Of course, I haven't reached this situation yet as my rising 8th grader is just 11, so take my advice for what it's worth!
