My sister (30 yo) and I (32 yo) have always had a tenuous relationship since we were in our early teens. In adulthood, we get in fights, then they fizzle out, then we would fight again, usually over stupid, trivial matters. This time, I'm pregnant for the first time after 2 rounds of IVF. She called me while I was at work and at first we were having a funny conversation. Then it took a turn, where she started saying messed up things about my relationship with my mother. I kept telling her it isn't the time to talk about that, she knew I was working and she just kept talking and talking about it until I had to hang up the phone on her. I texted her and said "Thanks for turning our funny conversation into a fight". She then went OFF on me. Called me a "fucking psychopath", "crazy bitch". Said she wanted nothing to do with my babyshower, and proceeded to say she doesn't want to be the godmother. I didnt respond with any hatred or anger, I simply said, "Nice, you escalated. Not me" she proceeded to block me. We haven't spoken until my mother started getting upset that we won't acknowledge one another. My mother started stressing out about the babyshower, etc. But I am putting my foot down until I receive a sincere apology, especially since she said she didnt want to be the godmother anymore, which I think is the worst part of all of it. I told my parents that if I don't receive an apology, a different person will be the godmother, as heartbreaking as it may be for my sister to not fill that role. My father got involved and got her to send me a text that she considered an apology. It was clearly an AI written empty text that included no details of our fight and didnt explicitly apologize for saying she didnt want to be the godmother. I even plugged it into multiple AI detectors which actually said 90% AI written. It was offensive, empty and insincere. I told her i wanted nothing to do with her unless she calls me and apologizes. I feel that if she cant do that, she cant meaningfully fill the role of godmother to my unborn child. What kind of role model will I be to keep allowing bad behavior without setting standards for myself and my family in our daily interactions?