Not trying to take it serious but I’m kinda hurt

My niece has behavioral issues and yesterday everything was fine until her little sister came over today. I don’t know if she’s saying this out of jealousy etc but she started saying I don’t like you and I’m gonna buy a poster saying no aunts allowed, anyone can be in my room but you because you think you can go to my room with out permission and touch my stuff. She has the ugliest attitude, she’s 8 years old , her mother didn’t raise her my grandmother did but their parenting is horrible so they won’t really care about this. I live with her and try to be there for her 100% and discipline her because no one else does. But how do I deal with this ? I didn’t know what else to say so I just walked away until she cools down I guess because I know she’s gonna come back to spend time with me or help her do something