Interesting girl. She has a histrionic personality disorder and a little borderline. This doesn't mean that she's insane, but you have to treat her in a special way because her feelings sometimes (often) overwhelm her. Definitely don't be clingy, but don't freeze her out either (unless she's an ass unrelated to her mood swings) and be cool with whatever she does. (If you have mood swings, stay away from her because bad stuff will happen then!)
What-ever she does, try to just ignore her mood swings. Sometimes she really really wants, and sometimes not. Just be cool about when she doesn't have any interest and definitely don't try to make her feel bad (like you would with a normal girl). When she isn't in the mood there is nothing she or you can do and even things like explaining that she's missing out on something will do nothing good. Saying things that she missed out on great sex when she is feeling that sex is the worst thing in the world, is of course not good.
And don't try to make plans! If she's in a bad mood, there is nothing she or you can do. What I do is that I make (at least) two plans: One if she shows up and another one for when she doesn't. It's really hard, but it's nothing personal when she doesn't show up! No use to try to punish her, talk about it or try to make her jealous. See it like this: If she suddenly doesn't want to see you, she's doing you a favour because she's in a so bad mood that you really don't want to see her either.
But I can tell you than when she really is in the right mood, you'll see passion you never seen before
I have and have had some borderline girls, and I love them because they are never the same, stuff happens and it's like being with a big group of different girls actually.