just catching up with your sitch which is different from mine but our MILs could be twins.
I dont have any advice specifically on the sitch but the only way I found to detoxify effects of MIL was to treat any coms with her as if it was a badly run business (stay polite despite receiving long vitriolic emails etc) my sitch was painful with MIL as we were living in a flat she owned (paying rent etc although she was only "official" with being a landlord when it suited her - there are still repairs outstanding we reported 5 years ago) when I moved out after w had left (she went to stay with MIL) and rented a house she decided it would be fun to say there was no overpaid rent and a huge cleaning cost despite w saying she would sort all that in exchange for my moving costs (I was getting out quickly so w could move there as she couldnt afford rent anywhere of similar size)
What followed was a hate and venom filled exchange from MIL that went on and on. I just replied calmly paid her the cleaning costs and, blissfully, havent spoken to her since.
Loads about my W and MIL on my thread if it helps but the advice of Vanilla was priceless to me in that Its best to leave her to sting herself out like a scorpion.
Assuming your w and MIL have the same relationship mine do, (w is unable to break away from a narcisistic mother with a toxic relationship which even she recognises as well as her friends and my trying to help for 16 years) there is little you can do from your end bar sticking with schedules.
Its a difficult situation which has been better for me of late but with mil selling her place and moving in with w as a staging post before moving north I imagine Im about to have a second dose of interferance!
Keep going Alpha
Edz
M:44, W:46, S:10 M 13 years, T 15 BD:23/7/2014 W/S Moved to MIL: 23/7/2014 My new place: 21/11/2014 W/S back to flat 22/11/2014 W coming closer, talking 4/2015 Piecing 5/2015 Moving in again 6/2015