Personally I would want my M to persist somehow as it is a crucial time for my D at school. I am hoping that when the appropriate evidence presents itself I would threaten D (this time for real rather than the hypothetical conversation at the time of the last confrontation), enough to make her see what she is doing to everyone for real and pull back from the brink (I hope and pray).

Me 55, W 50
D 8
M 20
T 27
MIL w/ us
BD 01/02/17
workplace A (12/09/16, EA -> PA)
OM senior manager, long term W, child 14
now: limbo (my choice)

"Don't care what you may do, we got that attitude!" - Bad Brains