Nightmares about past

Hiya, my daughter (14 years) hasn't been sleeping well and having nightmares and flashbacks about her past. Certain things are triggering her now, which usually wouldn't, like certain words, smells, noise and food, even wearing some clothes and I'm getting worried about her. I explained before that she's been low and getting fed-up and doesn't have much motivation but the past 3 days, she's been tidying her room and sorting things out, which is great. 

She will not go to any places which remind her of the past, for example, forests, places down the road and parks. She's not been like this before but ever since Friday, one of her teachers triggered her and she left site and is getting upset by the things I've mentioned.

Basically she's had a low, hard past... It started years ago when we moved house and school, then she moved school again due to behaviour, 13 hours later, she went back to the other school and moved to the PRU she's in now, before Covid. During all of this, she did home-schooling, became depressed, had suicidal thoughts and behaviour, in and out of hospital and detained under mental health act for months because of leaving and doing runners. She was also arrested 1 month after her 14th birthday (there was a lot of police involvement months before), for possession of bladed article, 3 counts of assault on emergency worker, threats to kill and a public order offence. That all happened when she wanted to end her life and left home. After all of this, she had to live with her dad for months and we gradually had to up the time she saw us (she's now living with us full-time) and she was so close to being taken into care. I mean so close. One time she was in hospital, the social worker was about to call and take her away from us until her dad called and said that she'll stay with them. So that's her past and she's come along way and we don't want to go back. Unfortunately, like I said, she's having nightmares after being triggered and now not doing certain things. 

I'm sorry about all this but I really need help with her. How can I help her? What can I do? She doesn't want to go to school anymore but said she's only going to see a friend she just made, to do her cooking lesson and to do P.E (playing volleyball with friend). What can I do now? I'm trying my hardest but when we solve a problem, there's always another one... 

Thanks and I'm sorry again...