SIL heard me and my mom talking about her😬

My brother married my SIL last year. They eloped at the courthouse. We didn't even know he was dating anyone. We were having a family cookout and me and my mom thought we were alone and we were talking about her. She just isn't someone my brother would typically go for. He always went for slim girls really pretty girls. She's overweight and dresses like somebody's grandmother even though she's in her 20's. He's also always been into really feminine girls. She's not the most feminine. At least not from what we've seen. She works in a male dominated career. We've never seen her wear makeup. She's not conventionally attractive. I don't think she's SUPER ugly. But she is to comparison with his ex's. My mom said "I can't believe he has sex with her." Which I laughed at because it was a random thing for a mom to say. I didn't know she was eavesdropping on our conversation until they left and my brother reached out to us angry. Saying nobody in our family knows anything about him. Said that they don't owe us anything but part of her weight issues are her having PCOS and endometriosis along with thyroid issues. That we are shitty and called me and our MOTHER stuck up bitches and to not reach out to him or his wife again and to look in the mirror the next time we want to call somebody ugly. We obviously would never have said any of that to her face because we don't want to be mean. I'm not a mean person. I was having a private conversation with my mom that we didn't know she heard and eavesdropped on. My mom is heartbroken that my brother doesn't want to talk to her anymore. We didn't go out of our way to be mean to my SIL. We talked in private and she heard and then ran to my brother.