I am so sorry that your D15 is struggling big time with so many transitions: mother having MLC, moving away, changing schools, new set of friends, new environment. That's A LOT for a young teenager to take on.
Right now, it may feel like you're losing your D15...but truthfully you've already built bridges for her to return back to you later on in life. When I was 15, I didn't care to be around my parents too much. Thought they were "dumb" and didn't know squat about life. Ha! From my young adulthood years and on, I became much, much closer to my parents...especially my late father. Tight as a bug.
Hang in there....only way forward is through it, not around it.
