Am i right or just being bossy?

Im ending my ML soon in 2 days. And i just got to know my MIL who will be taking care of my daughter actually gave my Daughter an extra scoop of milk to her feeding as she claimed the milk is bitter. My daughter has alot of phlegm. I tried to tell my husband nicely to tell his mother off but he told me that what his mother is doing is correct as she had alot of experience with kids before. I can nvr had a proper communication with my husband pertaining my MIL as it will eventually led to an arguement. I understand mother is mother. My worries is..doesnt it causing her to have more phlegm Im soo stressed up now. We are not even paedatricians!