I don't understand her peculiar little behaviors

[Inflikted]

So there's this girl I know, and I fell for her pretty recently. She knows I like(d) her and want(ed) to date her, but it doesn't seem as though she reciprocates those feelings. I admit, I do still have some feelings for her, but I'm working on "getting over" her, I'm just not quite there yet. We're still very friendly with each other, though, but every now and then, she does or says something peculiar that kinda makes me wonder what she really thinks of me. For example, this is something that happened a few days ago...

 

I'm putting something together to do on a Friday night a few weeks from now with some friends (in fact, she's been helping me figure out the details, and is definitely coming with me and the group that night), and there are certain people I don't want to invite. In particular, there's this guy we know that I really don't like (he's a douchey "player" type that reminds me of some people that antagonized me a long time ago). I found out a couple days ago that she and this guy actually dated a little before I ever started liking her, but it ended badly because he was seeing another girl, too. They're still pretty friendly with each other, though, and I admit, I sometimes get a teeny bit jealous seeing them goofing around with each other. Anyway, before I knew this information (that they dated, I mean), I was telling her about who I didn't want to invite out, and when I said I didn't want this guy to come, she grinned at me, gave me this look, and slyly said "Okay". At the time, it seemed odd to me, but after I found out they had dated, it kinda made sense, in that it seemed like she knew I was aware that they had dated in the past, and that I didn't want him there so as to keep him and her away from each other.

 

If that's what she thought, though, how come she wasn't more... bothered? I mean, if that's why I had done it, that seems like it would've been a creepy and/ or "dickish" thing to do, on my part, yanno? Like I'd be trying to "keep her all to myself". Why would she not be weirded out/ offended by that?