First of all, I know you are against her badmouthing her sister to you, but because you know both of them and you're the adult in the situation, you might be able to show your daughter a different perspective. I don't mean mediate, just offer insight.

Second, anime. I've been teaching 13 YO forever. So many of them absolutely love anime but think they're the only ones so they deny loving it. I do my best to get them together, but it's just...confusing to me. When we had fun Fridays the Anime option always filled up first. When we had online clubs during the pandemic, Anime was one of the most popular. You're spot on that if the school starts an anime club, students will come.