Feeling shattered - what more can we do to help our daughter?

Our daughter is the oldest of 3. She is 13, then we have 11 years (anxiety) and 6.5 years (diabetes type 1).
Our daughter is in year 8 and has struggled on and off since she was little with anxiety. Last year 2014 she was diagnosed with anxiety and depression.
Our daughter knows we love her and she says she knows and feels we support her however she doesn't want to feel this way anymore. She doesn't want to be depressed and anxious about everything.
Last year she started self harming and started to see a psychologist at head space. Things began to improve.
This year her anxiety and depression got worse and she struggled more and more. Term 2 she hardly attended school and hardly left the house. She started to self harm again and began having suicidal thoughts. This is when we made the decision to start medication. She continued to see her psychologist however the sessions where with me and I would talk the the psychologist and relay things that my daughter had told me from our last session.
She talks mainly to me however can not give me a reason as to why she feels the way she does. She says she isn't bullied at school and I know she has a lot of friends who love and support her. The teachers at the school are also amazing and have been supportive. She HATES going to school. She wants to be alone but then feels so lonely - its the viscous circle.
My husband and I want to do everything we can to support her. She is so caring and generous, she has an amazingly big heart and would do about anything possible to help a friend or family. She is talented and beautiful however doesn't believe it.
Have anyone else out there felt so lost and like a failure? We would do anything to have her see herself like others do. Our heart is shattered and aches for her.