I don't think you're the asshole I feel like your sister needs to be more transparent with you like it's fine if she doesn't feel like hanging out with you that day but she should at least say hey I can't hang out however I might be free in so-and-so day instead of saying that you're trying to guilt trip her unless you're constantly telling her like every single day here let's hang out a little thing out but still I feel like there should be a little bit more transparent