Annoyed with belly touchers

How do you keep people from touching your belly? Specifically family. More specifically, your mother? I do not like to be touched. I’m not an affectionate person, except with my kids and husband and even the husband doesn’t always get the affection be deserves. My mother and I aren’t very close at all. I have a lot of anger and resentment towards her for somethings. She has never been there for me. This weekend is my baby shower and I will see her for the first time in 2 years. Talking with her today she said “be prepared for me to touch that belly” I said “no I don’t like people touching me, I will let you touch it once but that’s it”. She proceeded to tell me that it’s her right and she can do what she wants. I said well looks like you will be getting your feelings hurt. I am now dreading this weekend. Any advice?