My soon to be mother in law drives me absolutely crazy

I love her to an extent but she drives me absolutely crazy. Here's the story when I was 5 months pregnant my bf passed away (he's now 1 1/2 yrs old) after my son was born in Jan in Feb I started dating this other guy and his mother has been completely in love with my child to to point I don't even see him anymore for the fact we live in the same house as her. She'll even take him out of his crib when I'm sleeping without me knowing or just say without asking he's sleeping in my bed tonight. She babies him all the time to the point where he doesn't even listen. My fiance tells her to knock it off but she doesn't listen to any of us. The crazy part is I'm pregnant with her actual grandchild and I'm afraid she's going to do the same with this child