Should I tell my cousin to mind her own business?

I went to a 50th birthday party on Sunday. I was sitting next to the birthday girl (my cousin), and she mentioned to me that she saw my sister-in-law (she is married to my brother, I am estranged from her, my brother and their kids for 6 years now) who told her that my brother has some sort of heart problem. so my cousin relayed the message to me and said, "I don't know what you want to do about it." I told my cousin that he owes me, my mom, and another brother an apology for making our lives miserable for no reason (the story is too long to go into here), and I also told my cousin about all the people who agreed with us that my brother was totally wrong in what he did. Additionally, I told my cousin my mom has a heart problem also, which she wants my estranged brother to know nothing about, and then there was dead silence between us after our conversation ended.
When Mom and I came home from the party, Mom told me about my brother's heart condition not knowing my cousin told me about it, my cousin told her also, which really annoyed me since my cousin knew about our estrangement. It's sounds like my cousin is trying to get us all together again using my brother's condition as an excuse, and if my Mom decided to contact him because of what my cousin said, I would never speak to my cousin again, and maybe not speak to Mom either.
I kind of regret I didn't tell my cousin to mind her own business and I have no interest in my brother's life because I don't consider him family any longer and have no intention of reconciling with him, instead of just acting defensive.
I'm going to see my cousin on Thanksgiving and if the subject comes up again,
I'm afraid I will get angry and tell her to mind her own business.