Should I be worried that she didn't message me back?

[James]

I did some little flirting with her on facebook for like a week (I liked her new profile picture, we had a poke war, commenting random google images on her wall for like an hour lol, etc) and then Monday she poked me, and I poked her back, but now she hasn't poked me again since the (she's usually almost never on during the school week though, last week was weird). I wanted to ask her to hang out this weekend sometime, so then two days ago (Thursday) I saw her on and I said "hey loser" to her on chat, but she didn't reply and it turns out she didn't even see it until last night (Friday). Should I worry that she didn't message me back? I mean I wouldn't message someone back a day late if they just said "hey," so I don't think so. And should I try messaging her again tonight or should I wait a day or two longer?
Thanks
PS I know that just because I flirted a bit with her doesn't make her mine for the taking, but it just seemed weird that she abruptly stopped all contact. And I know that this should be a pretty insignificant thing to worry about, but I just really like her, I guess.

Oh yeah and a few weeks ago something similar happened where I sent her something and she didn't reply and then that time she replied 5 days later. Although that actually had something to say, it wasn't just "hey" (I sent her a picture of a turtle and told her it looked like her...that was the first time I ever got flirty with her)

[Brian]

Ahh, i know what you mean. It happens to me too, where I send a playful message and then think that she may have taken it the wrong way (it almost happened today).

Don't worry about it. You've probably told yourself that a hundred times already but just stick with the idea that she couldn't possibly be so shallow, ESPECIALLY after all the flirting shared between you two