MIL wants to be called “Mom Mom”

Apparently this is the name that MIL's mom used for the grandkids. MIL's mom has now passed (I never met her). She wants to be called Mom Mom for my LO but I'm not a fan of the name...she's not my Mom so she's not the Mom-Mom of my child. I think she just wants "Mom" in the title so she can claim that my daughter can say that word. You can see my post history for the crazy narc this lady is.

She has her sentimental reasons for wanting this name but I want her to pick something else lol. Is that mean?