Furious!

I need some advice! My boyfriends dad has a 26 year old girlfriend soon to be wife, and I'm 21 and my boyfriend is 22. Her and his dad say she's going to be my baby's grandma.... I hate that!!!! She's not my baby's grandma!!!!!!!!!! I'm not okay with it at all. I've only know her for a short time! It bugs me! How do I go about putting this out there !??!