Mom badmouthed my niece and my sister heard it

[Anonymous]

If you look back at my old topics youll get a better idea of what I have been dealing with regarding my mother. This holiday i went to visit my mom and we spoke to my half sister(this matters) . My sister tells my mom her daughter was finally in her 30s graduated college and has her own apartment. My mom told her that was nice(we havent seen my niece since she was 5 im not in my 40s)and hung up. I told my mom I was so proud of my niece and my mom blurts out " she lives in low income housing with ten kids i bet" I was stunned and told my mom thats an ugly thing to say...but this is the kicker my mom THOUGHT she hung up but didnt and my sister heard her.Now shes not my moms daughter (see told you clarifying shes technically a half sister is important)and she was barely around her when i was growing up. Ive been trying to figure out what to say. I want to apologize but I didnt say it , but I still feel bad. How should I handle this? My mom isnt going to apologize that ik shell deny it. So what should I do? Wait for her to bring it up?  I was astonished ...