Mother in law.

So not exactly for sure what group to put this in...but my mother-in-law decided to walk up in my house today and stick her nose where it didn't belong when her son and I were having a small argument. . My son was supposed to go with his father and her for a bit, but as soon as I found out she had been putting my two year old in a booster seat I said no and took him from her. Mind you, my two year old isnt even at the weight he should be..he is a skinny little dude just like his dad and only weighs 24-26 pounds.. So since I took my son from her and wouldn't let him leave with them she decides to call me a little bitch so on so forth and brings up my moms past and basically says having him around my mom is putting him in danger. Mind you my mom is clean and sober and basically works everyday. The argument went on and on, and to the point she demanded her 22 yr old son pack his things and move back home with her. so tell me this am I wrong for verbally defending myself towards her today?Let's hear your opinions. (Not the first time she has gotten into it with me, just two summers ago she was telling me she was going to kick my teeth downy throat.)