I absolutely love witches (can't say if it is related to being a lesbian), so I hope it wasn't used only as a device to get the character in a different world. That being said, I'm kind of confused as to why Rosé was so fascinated with the clothing. It doesn't seem that different to what people in her old life wore and she's dressed like she came from another high school.
Yeah, it was a little odd for her to be so fascinated by what wouldn't have been too different from her presumably European-style fantasy world but to have no issues with speaking/understanding Japanese and using chopsticks.
okay I'm glad this is just the name of a place, not something else I was totally not thinking of
Also my first thought, though thankfully I already knew that Sado is a place so it didn't take too long to figure out :v