When you blow off her contacts, DO NOT RESPOND LOGICALLY. It will do no good to use the reasons you've stated. Instead, mask it in indifference and a seeming lack of interest.
"Oh, I got busy talking to this girl I met and didn't see your message. Did you still want to talk? I might have some time later."
"Oh, I got busy talking to this girl I met and didn't see your message. Did you still want to talk? I might have some time later."
Because I said so.

