child calling MIL Mom

My MIL keeps saying that my unborn son is her "baby" (first grandbaby) I didn't think much about it I actually thought it was cute until she started saying that she's gonna let him call her mom cause she's gonna be his mom too which makes me kind of mad due to the fact that she was being bitchy when she found out I was having a boy (she really wanted a grand daughter) even rolling her eyes when family members asked what i was having. I don't wanna seam like I'm over reacting but it makes me mad how fake she acts. What would you Do? (we live with them for now btw)