Hi Deeply I've just joined Mumsnet as I felt compelled to reply to you. Your daughter was me, I lost my dad at the same age and I went from being a happy teenager with good attendance at school to a very sad and lonely young woman. Please get her an appointment with GP to see what they can suggest, is there one Doctor that she is more likely to be open with? Although I would be wary of anti depressants I was prescribed these and I think they made me feel worse. I also struggled with counselling it did seem pointless the counsellor didn't seem to understand and I didn't know how I felt so how could I explain.
I really struggled attending lessons although I didn't leave my attendance was very poor.What helped me was a incredibility understanding head of year, I was allowed to do half days and wasn't called up on my lack of attendance or lack of work, this actually helped me knowing that someone understood and I wasn't going to get in trouble. Have you spoke to school and things in place to help her? At times like this it's not just about how much work you're doing it's how you feel even if she had to drop a subject?
Has she got ay hobbies she really enjoys, is passionate about? For me it was horses I was very lucky that my Mum bought me a horse after my Dad died and honestly say I don't know if I'd be here if I hadn't of had something to concentrate on. I had something of my own to love and care for, it didn't matter how bad I felt I had to get up on go down to him. I'd often walk out of school and go riding instead, no I wasn't in school but it was my therapy . If there's something she is into or showed and interest in before she lost her Dad I would suggest try getting back in to it. School is important but so is mental health and this something that really really helped me.
Also I'd suggest maybe counselling for yourself, so you know the best way to help her. My mum saw cuts on me and never asked what was wrong, she wasn't a bad mum but had so much to deal with herself she didn't know how to deal with me. Most of all be there for her, let her know she is loved all the time, which I'm sure you do anyway but I remember feeling like by the time the grief hit me my Mum was over it and didn't seem to offer a lot of comfort. Please feel free to send me a private message (sorry I don't know mumsnet only joined because of this post, but presume you can) As I remember how I felt and if my experience can help you and your daughter slightly I would be willing to share with you, as it was a horrible time.
Just to give you some hope though, I came through the other side although it has taken a long time. I now have a good job, go out a lot with friends and it doesn't control my life anymore.