Ah, good ol’ misunderstanding comedy. She didn’t even notice that the way she was wording things sounded exactly like typical disapproving love rival dialogue.
I don’t think it’ll happen in this story, but it’d be nice to see an isekai where the main character has an antagonistic but positive relationship with their sibling. Y’know, the squabblesome kind where you fight over food and hate each other’s guts, but have a shared feeling of camaraderie nevertheless.