How to unfriend someone?

First of all, she's almost crazy and a little back stabbing. Once she found out who your crush is, the next thing you know they're besties forever, it just kinda feels wrong you know? Plus, she could get mad and all sensitive when she borrows a book in school and I ask whether she can put it in the middle so all four of us can share. She was pissed at me for that too.

I have also concluded I didn't need friends like this in my life. So I started distancing myself from her, only talk to her when she asks me something and that was it. She doesn't sit beside me, but she does sit beside a good friend of mine. And that friend always gets bullied by her. I decided to give my good friend some chocolates to brighten up her day. That's when the lunatic went crazy when I didn't give her any.

Should I continue ignoring her?