I was in just this situation at her age. My advice is not to pressure her about school. She can always go back to education later (I left after GCSEs and now have a Masters degree). Mental health is much more important at this point - it's harder to fix later!
What helped my confidence was doing voluntary work - you feel like you're helping people and because you aren't being paid, there isn't the same level of pressure over getting everything right. I did that for a year part-time and then found a full-time job in the same area, confident then that I had the skills to do it.
Counselling helped me, but only once I was over 18 - I felt as if I were taken seriously then, whereas before I was treated as a child who needed to be doing what all the other children were doing. That approach really didn't work for me - talking about organisational skills to help me back into school was like rearranging the deckchairs on the Titanic when I was suffering a genuine existential crisis and didn't plan on living much longer.
I can imagine this sort of thing must be really tough to deal with as a parent, but if you can, try to support her. If she's anything like I was, when you say 'please tidy your desk' her brain is twisting it into 'you're so useless, look at what a mess that desk is, it's disgusting' or something similar - and then dealing with it becomes overwhelming. Which isn't your fault at all, but it's what depression can do sometimes. It's not personal, even if it feels like it.
Obviously everyone is different and some of what I've said might not apply to your DD - just wanted to let you know that even if it takes a while, it's possible to come through it and have a happy adult life.