AITA for telling my sister she shouldn't make our 68 year old mother think she failed as a parent?

I have given her nothing but support. If I was like her I would have never forgiven her for some of the shit she's pulled. But I look past it because she's my sister and I love her. I edited my comment and replied to your reply on said comment because I realized that it was out of line. Believe it or not my relationship with her is/was better than the one with my older sister. We play boardgames together. Everyone else in my family won't play them with me. Part of my frustration with this situation is that, because I'm the baby, and because I like to joke around, my sister's get away with disrespecting me while I'm expected to blindly respect them.

/r/AmItheAsshole Thread Parent