Maybe I need to see the rest of Catherine's supports (I didn't use her in my Silver Snow run), but I really don't read her as a bottom. To me, Catherine and Shamir are a textbook switch couple. I really don't see either dominating the other because their personality types are too evenly matched. If I had to pick, though, I'd say Shamir is the bottom. She's a major tsundere who talks a big game.