There are a few issues you have identified:
She has some homosexual feelings.
She is exhibiting what you identify as an unhealthy obsession over another person.
She is on antidepressants.
She is in therapy.
She has stopped going to school.
Because all of those items are in one question, the natural presumption is that they are all related. From my personal experience as a gay, bipolar, ADHD person, I rather doubt everything in your question is related, but that's for your therapist to be the authority.
Taking a step back, each issue has its own items to inspect:
Having homosexual feelings isn't always the most devastating thing in someone's life. Because of social stigma's, lack of societal support in many areas, a lack of knowledge about homosexuality, and other factors, the "coming out" stage varies in difficulty significantly. It is also well accepted in the "gay community" and amongst many others that sexuality is on a range from completely heterosexual to completely homosexual, with very few falling at the extremes.
Many communities have support groups for teens identifying as homosexual and those who support them. If your area has such a group, it may be very helpful as she will then be able to spend time with "others like her".
An unhealthy obsession over another person (regardless of gender) is something many people have to work through -- whether over a celebrity or the hottie at school. It is important to work with your therapist to help your daughter establish healthy, balanced relationships with other people.
I will not address the antidepressants as there's only one way she's getting them and that's through the psychiatrist prescribing them, so it appears to be being addressed.
The other posts have discussed supporting her and working with her therapist. I will only add to be sure that she has confidence in her therapist (i.e. she relates with him/her and feels that the therapist relates with her.) Without a trust bond between patient and therapist it is unlikely the therapy will prove therapeutic to the degree desired. There are many doctors, so find the one which will help her most effectively (if you haven't already).
Not going to school is, perhaps, one of the more challenging, immediate components of your question... she is most likely in fear of ostracization and bullying. Alternative options likely exist: a different, somewhat-nearby school? home schooling? Chatting with the school principal could be quite helpful in resolving this. A change of venue is often helpful. I do, however, recommend discussing this suggestion with her therapist first in case there are other aspects of your question not written above (and, well, even if you had... I'm not there to see and I'm by no mean a therapist!)
One thing I notice which is distinctly missing from your question is what your daughter says/feels. While everyone is recommending talking to her therapist (a good suggestion), talk with her, too. -- And by that, I mean to just listen... she has plenty to say.
Finally, you say that the issue isn't "solved" -- it will never be solved as it is not a math problem. Your goal should be to find a resolution to what is ailing her so that she can live a healthy, productive, balanced life.
And, in that goal, I wish you both the best.