My sister in law

Tried to give my 4 month old chocolate off her finger after dad and I said no sugar till First birthday. She came at him and we both said no and she says oh he's fine he can have chocolate. Ugh she drives me crazy she acts like she has a say I feel like I constantly have to remind her that he is not her child and to butt out. Luckily we stopped her and she didn't give him any cause I think i would strangle her