Basically echoing what everyone here is saying. There may be a very good reason for her / her assistant / her agency's poor communication, but that doesn't excuse it, if that makes sense.
To answer your final question, you don't owe her anything, and honestly, just don't bother and move on. That may sound mean, but this is real life. Sometimes things slip through the cracks. Communication is like a game of hot potato, and she's the one choosing to not toss it back to you, not the other way around.
On the off chance that, let's say she (or her assistant / agency) DOES get in touch with you with concrete appointment details at some point,obviously it's your choice if you wish to proceed with the date. But you have every right to politely say something along the lines of "Apologies, but I didn't hear from you for X # days, so I did make alternative plans. Hopefully, our schedules can align at a later date. Take care!"
