Sister said I should have defended her when my mom "mom shamed" her and told her that her son's are better off without her

I didn't defend her because my mom didn't tell a single lie. My sister got pregnant on purpose at 16. Had my nephew's at 17. They 15 now and she is so immature and almost never has her kids because she rather be out being a dumb ass. Her baby daddy's parents have the boys because her baby daddy's heath is way too bad and he's probably gonna die within the next year. She is never there for them. When she does have them she's too busy twerking online to TikTok dances to pay any mind to them. People online call her a bad mom and she loves it. She got herself a jacket that says "Bad moms". She completely leans into the bad mom thing. She's embarrassed her son's because she posted on her Twitter sexual stuff with one of their friends. The kid is 18 but when you're in your 30s it's weird and predatory. She's on Instagram shaking her ass on her teenage sons friend. She has ditched her kids to go have sex with their friend. Then post NSFW stuff online and they get made fun of because this kid is showing videos of him fucking their mom to others at school and my sister loves it. She loves the attention. She doesn't care how what she does affects them. She doesn't care when she embarrasses them. She will pick boys, I'm saying boys not men because she's fucking 18 year old high schoolers not men. Well now she's going after men closer to her age at least. She got bored with the high school. She also constantly puts them down. When one of the twins fell in love with dancing My sister accused him of being gay. She told one that they were the less attractive twin. She's awful to them. My nephews turn 16 next Month and my mom is working on the party with my nephews other grandparents since they have custody and my sister said she won't be there because a man is taking her to Disney world. My mom snapped at her and said "Good. You're a terrible mom and they're better off without you." My sister laughed and accused my mom of being jealous that she can get any man. My mom told her to get out. My sister texted me saying I should have defended her. Should I have if I agree? I do think she's a bad mom and her kids are better off without her. She adds nothing good to their life and she's the reason they're in therapy. She's awful.