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.
@colboh You should read this fanfiction because you will love it, and more as it is building that kind of relationship Yuri that I agree with you between Enty and Bel.
The fanfiction is not mine if not the respective author whose username on that page is Salvo519, and I'm reading that story but I'll give you the link so you can read it if you wish.