I fail to see the problem.

Like, I genuinely can't see what's the problem not-Goblinslayer person here is trying to convey. And I'm strongly inclined to believe that whatever point you might try to bring up, my reply will be Finn's "that's the opposite of a problem" pic.

I think I heard somewhere the Japanese strongly value femininity in a woman. If she is shows too many masculine traits, something is wrong with her and she will probably not make a good wife. The general society outside of manga seems to like to put things into boxes, and are bothered when they break the mold.

Also, she has no interest in Goblin Slayer. She's asking this because she likes this other guy, and is nervous about him being not being interested in her.