Popping my head in again, after falling off the page rather lately.
Huge hugs to you and your DD, pasanda. I'm so sorry to hear you're going through such a tough time. DD has ADHD and gets very down at seemingly random times, for reasons she can't explain. We are lucky that she has never self harmed but she experiences feelings of self loathing, which is hard to watch. In the 10 years since she was diagnosed, we have never been referred to any kind of MH agency, surprisingly.
ADHD is so often missed in girls, and anxiety and depression is a very common co-morbidity, so I'd definitely try to get her assessed if at all possible.
Funnily enough, DH had wondered whether he too has ADHD, since recognising DD's traits in himself. A couple of months ago, he finally plucked up the courage to talk to our GP, who referred him to the community mental health team; he had to fill out an assessment form and then had a telephone consultation, and is now waiting to be referred to psychiatry. I could say he self harms, but it's not in a physical way, if that makes sense?
I really hope you can find some answers and support. 
Life rolls on as normal/new normal here. DS still hasn't been able to work since March, though he does have a day of rehearsals next week. DD says she's doing fine at school, but has also made it clear that we're not to get involved with homework or anything else; even asking her about school work results in rolled eyes, heavy exhalations and protestations about "privacy".
The contrast from earlier in the year, when I was required to sit with her and take her through every revision session is quite extreme. Problem is, we know that she's not capable of keeping on top of things, so things have become pretty tense between us all.
In addition, she has become addicted to her phone, snap chatting and whatsapping her friends and the notBF constantly, and her free periods are spent messing around in the 6th form common room. She's already decided psychology is not for her, nor is an EPQ, but she has no idea what she wants to study at uni any more, so doesn't even have that motivation to keep her working.
It feels like she's hit the horrible teens later than most kids - her view of what's reasonable behaviour from us, and her, seems more like a 13 year old's. It's exhausting and stressful.