Keeping Grandma at a distance!

My husband has expressed for our daughter's next jab because he can't stand them and doesn't want to be there, for support he wants his mother to come with us instead. I've been like whatever but then he told his mother and she's up for it and messaged me to let her know. To which I told her it's not going to be now. She also says he has to pull through it instead of avoiding it. I agree to that. Even my my LO has a great bond with grandma, I don't want to include her in everything especially when it's the parents decisions or responsibility to take care of things. To avoid any arguments I've been thinking when the time comes I'd go there alone without her knowing. Or should I let her know?