Another possible explanation for her 'bizarre' behavior: She's trying to move on and interact with you as a mature adult in situations that would normally make her uncomfortable. I mean, seriously, if an ex of mine showed up at some event I was at, what am I supposed to do? Act like a vampire that has had holy water thrown on it, and run screaming from the building?
No, I'm going to go about my business, and if i had to interact with them, I'd try do so in a polite manner.