No dont get involved, just stay neutral.There could be reasons she feels justified in this (could it be her parents both knew she was autistic, and kept it from her, for example?, or at least her dad did, but mother thought she knew?)- or it could, as you say, be her mum making trouble- in any other way- but if she has done similar (by 'taking off') in the past, then try just wait & see, it may all just blow over as suddenly as it came.All you can do is be there for them both really, and at least your son gets to know she's ok, through you.I too don't understand why she texts, etc. if she isn't talking to her dad, but unless she brings up the subject first, its hard to broach that subject without her falling out with you too..just tell your son to try ignore it to an extent, she's just venting her anger i guess, much like a stroppy teenager would?- he might benefit from the counselling himself, and one day his daughter may eventually come to agree to it, you never know.If not at least it may help him understand a bit- can he find one who specialises in autistic relationships? It may help him understand why she is as she is towards him??