Baby shower drama

Soo, here’s the thing.. my mother in law has a sister and I really don’t like her… she’s been very mean with my mom (they kind of worked together a few years ago while I was engaged with my now husband).. she actually tried to make my mom to be fired and all that (she knew who my mom was and the familiar relationship and knowing that she did what she did)…

Now, I’m pregnant and my mother in law wants to organize my baby shower and I am 100% sure she is going to invite this person (duh! It’s her sister!) but I really don’t wanna see her that day (nor any other day actually)… what would you do if you were in my position? My mother in law does not know any of this (I never told her what she tried to do to my mom) but I absolutely don’t want her invited.