Am I over reacting?

So my mom is paying for and throwing me a baby shower and since it's somewhere nice I'm working on keeping my numbers low...I'm personally not inviting certain friends to help my mom out. But my SIL who I have tons of issues with is now whining that she has to invite her new BFF (who she has only known for 6 months) to my shower. She even went over me to call my mom who can't say no to anyone. I know this sounds selfish but why should she be allowed to invite a friend who doesn't even know me? If she was having a shower I wouldn't ask to invite my best friend it's insulting. I also hate these hormones that upset me so