I have never quite seen eye to eye with the MIL, but tolerate her passive aggressive superiority because my DC love her and her them. My DP asked her to babysit Ds2 (5 months) for a few hours today while DD (10) and Ds1 (5) were at school, so we could go out for lunch together. It was the first time we have been out alone since he was born, and I was very grateful to MIL for agreeing to have him. Ds2 is ebf and has never had formula, so I expressed enough milk for her to feed him while we were gone. After a lovely lunch with Dp we went to MIL to pick up Ds and he was fast asleep (he should have been hungry by this point). MIL looking very pleased with herself said "The milk you brought looked funny so I threw it out, but Its ok, I brought some formula from asda the other day just incase, and look at the good its done him!" 
MIL has been anti breastfeeding from the start always dropping totally unreasonable helpful hints on how ff would help Ds sleep better and would give me a break, ff is more socially acceptable, Dp won't bond properly, he is too big to still be breastfeeding etc etc etc.... DP is very supportive of breastfeeding, but he and his whole family won't stand up to his mother no matter how wrong she is. Poor Ds has been sick a few times and is very uncomfortable now. I am in no way against ff by the way, just the way my MIL likes to control things all the fucking time with my dc. I could write a whole novel on her behaviour over the years. 