Crazy / *****y girls are basically looking for drama, and drag people right into their chaos and lunacy. That is their goal, and how they keep the cycle going. Most of them are miserable and insecure. The more you feed into it - the worse it gets. These people actually want to fight, and will continue fighting forever. That's why they keep causing problems and acting like *****es.
I've dealt with this for many years in the past. The more I fed into it - the more miserable I became. Thats what miserable want - to see everyone else suffer, and get caught up in their bull****, so they themselves can keep suffering. Yeah, its retarded. They also want to feel important, and purposely get under your skin to accomplish just that. They want you to be bothered by them. You'll generally find them causing problems with everyone under the sun, and trying to get them all caught up in their bull**** drama, so that they can keep fighting with everyone.
Your best bet is to just accept her as she is; realize that she's not worth anything; and treat the situation accordingly - as if she doesn't exist. Otherwise, you're feeding right into it, and giving her what she wants. Even if you don't fight back, getting upset means she got under your skin, and is bothering you. You even show-cased this when you asked why she was such a *****. Score for her. Then, she acted like an even bigger ***** to make you more upset, and keep her in your thoughts. It's still bothering you. Score 2. Let's not have a score 3. Out of sight and out of mind. Stop making her important, because she isn't worth anything. Any further response on your part will be matched with more *****iness and craziness. Round and round it goes.
You can't let people like this get to you. It's what they want, and it makes you feel like ****. Never obsess over losers. They're not worth it. They ARE going to get under your skin - because that's what they do. Gotta shrug it off and move on.
As for your friend, or whoever - he's clearly a dumbass. Everyone thinks the person they are dating is nice, or that they're nice underneath it all. A ***** is a *****. His turn will come eventually. It never fails.