When to know when to just give up or keep pursuing?

So my date with this girl was cancelled pretty late last friday by the girl. She did say she wanted to reschedule and to just let her know when, all good right?

Here's where it gets odd though. I messaged her on FB (She has an iphone I have an android, text doesn't work well) and asked if she'd be interested in doing something next friday? That was 3-4 days ago and the message still says unread, but clearly she's been on FB recently. What are my options here? Is she avoiding me? Could she have seen the messages and just isn't responding (even though FB says she hasn't read them). Need some help! Chase or Lose her?

Added (1). She cancelled cause of a wake, which she swears was true after I kind of let on that I didn't really believe that lol

She may be a liar but um fb doesn't lie.

Move on you asked twice and she blew you off both times ---- don't bother

It sounds like to me she is a flaker. I had a girl do that on me. We ate together once. She kind of introduced me to her roommates. Then I tried hanging our again and she kept doing a rain check on me. During that time also she sometimes texted me as well. I got nowhere. My advice to you is play cat and mouse. Just don't talk to her anymore. If you see her ignore her.

Be straightforward. Tell her that you are very interested in her--by calling or texting, since Facebook isn't working--and that you'd like to get together again. Suggest times and activities. Also reassure her that if she isn't interested, you'd respect her decision, but you just want clarity. You might even mention that you sent her an FB message and don't know why she didn't see it.

If she doesn't respond to this by not answering the phone or texting back, send one last message saying that you are confused and disappointed by the lack of communication, but need to move on with your life. Date other people!