Sorry this is hard. I know you know I understand exactly what you are going through.
I know it seems like you guys have a lot going on, and you do, but if I had to take a educated guess? It's the alienation starting back from mom again which is making SD need to lash out, act out what ever you call it.
I would sit SD down and remind her of her past problems, remind her how hard she worked to overcome them and how great the rewards were, honor roll, self esteem, better r/s with family, friends and teachers/staff, and mostly how much better she felt about herself. Show her the road she's on, and how to get back to the road to sucessful behaviour.
I do this with SD7 and it really hits home. She sometimes will even tell me she is suppposed to "make trouble" during dads time to "even" out the score according to mom, but we gently remind her that mom isn't suffering the consciquences SD is and why would her mom want that for her child? I tell SD she must have misunderstood BPDm
Hey what ever works!