WIBTA for suggesting my stepmom stay home from my graduation?

I (24F) am in my 3rd year of a mathematics PhD, and only have dissertation writing left. Since I did not get to walk for my BS (bc of Covid), I told my parents I would just make my PhD ‘the’ graduation. Of course I would invite everyone, send out announcements, hire a photographer, yada yada.

So far, I plan to invite my dad, bio mom, step mom, and two sisters, as well as my aunt, uncle, and any of their children who wanted to attend. When discussing this with my dad & stepmom, SM interjects and tells me to make sure that my dad doesn’t have to interact with my mom at all (they’ve been divorced since I was little and recently got into a small fight that upset my dad). I told her no way, it is not my job to handle who sees who, especially on a day that I worked very hard for. SM also mentioned she and my dad were going to make dinner reservations at a fancy restaurant and that my mom wasn’t invited. I also declined, saying that everyone is here to help me celebrate this important milestone, so we either celebrate together or don’t celebrate at all. She doesn’t get to dictate how I celebrate my special day by any means. I suggested that she should consider just staying home if it was going to be such an issue , but AITA for saying this & not conforming to her demands?