I'm going to throw something I borrowed from a friend in the rubbish
Did it break or something?
She doesn't deserve it back. She never calls me, she's self-centered and she's not funny.
Being upset with a friend because you think they're ignoring or avoiding you is fine but that doesn't give you the right to throw out things that you borrowed. You should always return something you borrowed and in this case you can use it as an excuse to find out what's going on between you two.
I don't have time to deal with her.
If you don't have time for her then give her her stuff back. She's only going to bother you for it so it's better to give it back to her now.