Mother in law help

Hey so I'm actually a soon to be dad & I have no idea on how to tell my girlfriend who is living with me & our daughter is on her way & I don't know how to tell her really anything that bothers me. So we've been living together since January & I love it honestly but sometimes I guess I don't know it a mother & daughter thing but her mom constantly calls her every time. Like probably 4 times a day & they're long conversations & most of the times I just get annoyed with it. Most of the times the conversations are about a group chat & how her mom doesn't understand what they say so she asks my girlfriend. I mean her mom has another son it's not like he can't translate either. I don't know I'm probably just tripping or whatever but it really bothers me. It's just so annoying. This is probably the stupidest post ever but I just don't know how to tell her it bothers me. I don't want to break their relationship. Or separate them. I know this'll probably sound mean but it's true.