My crush seems to be online on fb but doesn't see my texts?

I sent my crush a message on facebook one hour ago ( we were already texting ) , she logged in ( on her iphone ) three times but she didn't reply, there isn't even the "seen at" message so, i'm sure that she didn't see it then. What i don't understand is if she is just ignoring my messages or not, i don't know how facebook works on an iphone. Might it just be that she didn't see the message even though she was online? Or just that the iphone logged on facebook getting wi-fi without her seeing the message? While she's online in these moments she doesn't like anything and post anything.

P.S. I know that she's gonna text back, she always does, but I don't know why when she's online in those moments she doesn't reply. ( Last time happened yesterday, she told me she was hanging out with her friends, i sent her a message, at 11 o'clock, and she replied this morning saying she was sorry because she fell asleep. )

Look, you're coming off as extremely needy and insecure. Just relax and be busy. You're life shouldn't revolve around one girl. When you act indifferent it catches our attention.

She probably saw the message notification but just didn't read it yet.