AIO over my stepmother using N-Word

Im not sure what to do or if im over reacting even though I really don’t think I am. First off all we have a kind of chocolate where I live that used to have the N-Word in it’s name but obviously hasn’t for a while now.

So I was at my half sisters bday today and my stepmom (let’s call her M) as well as her mother (let’s call her S) where there as well. It was a kids birthday party and they had said chocolate so M asked if anyone wanted another one of those things using the old name (with the N-Word) I told her that’s not what they are called anymore, she rolled her eyes and said she always said it and was not gonna stop, S jumped in and agreed with her and then M tried to argue/excuse it saying they where using that name in my Sisters preschool as well, I said well than they are apparently racist as well, she said yes but she was still not gonna stop and this was my problem.

Now I agree with her as far as her saying it’s my problem, I can’t force her to stop saying it (not the first time she used the N-Word not only regarding the chocolate and not the first time that I told her not to say that) but I can obviously set boundaries for me, but I know when I tell her that it really bothered me she will tell me I overreacted and that it’s not that bad and I’m being to sensitive.

Now am I overreacting? Or should I tell her again and tell her I will visit less if she keeps saying stuff like that?