Out of spite, I'm going to hurt the feelings of someone I care about?
That's not very kind, why would you want to hurt their feelings?
She wants to be the focus of all of my attention and drop all of my other friends in the process. I can't do that.
I hear what you're saying but it is wrong to intentionally try and hurt somebody's feelings. If you have any issues with someone you should talk with them and resolve them. Otherwise you will keep hurting people and will end up alone.
I'm acting out of spite, not because it's wrong.
Wanting to get back at someone for their actions is a normal feeling, but that doesn't mean you have to act on it. Rather than be spiteful, address the issue and let your friend know that the way she is treating you is unacceptable.