Overbearing MIL

My MIL is a very difficult woman. She's  very insecure and needs to feel needed. She lives four hours away, but whenever she's in town, she doesn't say much to me and she kind of takes over the motherly duties for my 3 yr old son. She feeds him, changes his clothes, wipes his butt after going to the bathroom and everything. She even answers when he yells for me. She's been like that his entire life. Anyone else have the same situation? What did you do about it?