Am I being a b!+@#

I baby sit my bfs 2 year old niece 3 times a week. Generally speaking she is a good kid. But lately she has turned into a monster. She doesn't listen to anything I tell her (like stop jumping on the couch, quit screeching, etc.) I don't have many rules at my house. I just ask she be respectful of my things and my dog (why I don't want her screeching, it gets him worked up). I have a toy box of toys/books that I have bought, been gifted with, or were mine when I was a kid and am giving to my unborn daughter. That's all the toys I have at house. Her parents don't bring any of hers over either, so I started letting her play with them. She is destroying them though. Especially the older toys/books that were mine. It's really starting to upset me. I have taken them away, put them up completely before she comes over, and everything... But she will throw a fit if I don't give them to her. She thinks everything in my daughters room is hers and wants to take things home with her. It's really starting to upset me. Her mom gives her everything she asks for and babys the shit out of her. Anytime she starts crying or throwing a fit her mom gives in to what she wants. Idk what to do.