MIL BS

Just want to vent. I have a MIL that use to love me and from the day I had my child has started a war. Basically she thought having a grandchild would revolve around her. When it didn't she got really nasty. So my husband stands by me and doesn't give into her unreasonable demands. We are having his party next month. Big party. Invited over 50 people. She told my husband that she doesn't want to come to our party so she will be throwing her own party. What?? What even makes her think she has the right? If it wasn't for my husband I would tell her to fuck off. I told him if she wants to have dinner with us she can and celebrate then. But no way in hell is she throwing a separate party because she doesn't want to attend ours. Am I over reacting?