MIL and how to keep her from thinking shes my child mom lol?

So this hasnt become a problem yet since my baby isnt due until September but just by the way she acts i have a feeling shes going to try to tell me how to raise my child which i am really not going to put up with. Shes already told me that he cant have a pacifier lol dont get me wrong shes a really nice lady and we get along great but her trying to tell me how to raise my child is not going to happen. Now here's the hard part.....because everything is sooo exepensive in Southern California my boyfriend will be working fulltime like usual and i will switch to 4 days instead of 5. For the 4 days that i am working my mom will be watching him for 2 days and his mom for the other 2. I am very very grateful that they both offered to do this but im wondering how i can still have her realize that her role is gramma and not mom when shes watching him for 2 days. I really dont want it to get to the point where i get so frusterated and have my mom watch him the whole week.