Hell Heather. I extend a warm welcome.
THis must be pulling at your heart strings; standing by watching this happen and feeling totally unable to help.
I have 32 year old daughter now diagnosed with Depression; but, I am sure this went back to childhood. It was a real struggle for me as I felt I was doing everything wrong as a parent. It never occured to me at the time that there was a reason for her mood and that it indeed was a problem I ought to have gotten her help for. I just thought she was being a moody difficult teenager. Oh how I feel rotten now.
What would I have done differently? I would have acted on my fears. I was by the way in my own debilitating Depression for which my then husband found reason to tease and abuse me about. The last thing I could have done was get my own help so I expect this was a big reason why I didn't get it for her.
You apparently are already in the system however and I applaud you for that. You are a good parent. You are doing what you can.
I do have a few suggestions. Maybe you have done these things already. If there is a Guidance Program at school, take advantage of it. Make it part of your daughter's treament program. Also, look for support groups - not just for depression or mood disorders but possibly for adoptees.