Well how about this.

Obviously she knows your situation and is still demanding more than you can offer. And I think you can't just keep giving in to her. Or else the relationship would be very much one way.

So why not, this time, don't give in to her. Just tell her that you can't make it. Don't talk to her until she calms down and is reasonable. Let her be the first to break this time. See if she comes back. At the worst, she'll break up with you, which might not be a bad thing anyways.