M.D.
I was always told if someone is talking about someone else with you, they are taking about you with others. Are you sort of doing that right now, don't take this the wrong way, but you are venting about her talking. It's bothering you, it bothered her about her son. She's just venting, we all do it if you think about it. I'd let it go, or just accept that all people do it. Maybe after venting about it, she can accept it later. My grandma wanted me to tie my tubes after I had two children out of wedlock, well, 9 years later I had my 3rd, with their father, just finally married. Did she ever say anything to me? No, but I heard about it, upset me a little at first, but I see where she was coming from.
You say you get along with this woman most of the time, don't let this bother you, I don't think it's worth it.