There are none so blind, as they who will not see. None of it your fault, and sorry hon, but I figure she is as much to blame as he is....as she blames the girls and he gets away free. Maybe this is part of where you AH's problems spring from, as it could be dad has been a lecher for many years and MIL has blamed everyone but him for it. Lesson learnt by AH was that was how it is, and he expects not to be blamed for his misbehaviors with drink.
Treat it as a sharp learning curve, for yourself and let it go, as if she does get back to friendly at some time, you won't know when she will turn agin you again.
God bless