She is sitting in the library, studying. It's her most common pastime, by hours; spending time with her sister is more enjoyable but Jaromira prefers to socialize more broadly and Katarzyna would only get in the way. This is better on net; the two of them share a room, so it isn't as though her sister's time is entirely hogged by the other girls who call this boarding school "home." Or at least "prison." Katarzyna doesn't mind it, though; the school library is excellent, and basic manners and care for the books has endeared her to the librarian to a sufficient degree to lubricate the interlibrary loans process when there's something she wants to read that they don't have.
Kanimir and Jaromira in Fabulous
fabulous_ones
"I suppose, but that introduces strictly more complexity than magical girls being a thing at all."
"True. I'm going to stop hypothesizing in the absence of fact, this can be a research project."
fabulous_ones
"Anything fun in school or does it all pale in comparison to crackpot origin of magic theories?"
"I like my science class. And English makes Jaromira happy and I like seeing her happy."
fabulous_ones
"Are you allowed visitors on your campus? Should I come by sometime?"
"On a related note, I thought of a less-low-hanging-fruit way of making money as a magical girl."