Poor girl, noscat, and poor you.
I've only got second-hand experience, but I'll share it with you for what it's worth.
My friend's daughter became sad, withdrawn, angry, unsociable, under-confident when she was fifteen. She was prescribed anti-depressants and saw a therapist once a week. This approach worked wonders for her and over a period of two or three months she recovered and regained her normal happy, confident,out-going, light-hearted self.
Six months or more down the line, the psychiatrist that she is under was happy to take her off the ADs (in January).
I have had my fingers crossed that the daughter stays well but my friend said to me just last night that she thinks that her daughter might be slipping back.
Maybe she needs to be on them for longer - my friend has long-term issues with depression and is on ADs and happy to stay on them for the foreseeable future. It may be that some people need to be on them long-term?
Not much help probably, but I thought I'd share my limited experience with you.
Good luck to you and your daughter.