Don’t touch my belly

Hello ladies! There’s this girl at my job who constantly acts as if she’s my mother always has an opinion and always wants to touch my belly. I sit down on purpose so she won’t touch my belly, but I need to find a nice way to tell her please stop touching my belly but not be rude at the same time. It’s getting annoying and the only people I will allow touch my belly are family and close friends. Please help!