It seems that you already probably have the answer, if her reputation is being a flake.  I don't think it has to do with you or the offer of a freebie.  If you've been around for any length of time you know that some girls just don't return calls, for a host of reasons.  Just like girls know that some customers flake out.  Nature of the biz.  It could also be that she got busted, sick, or other reasons.  I don't think any of us can tell you "what gives" in this case, but if you are persistent you might find out.  Or maybe not.

By the way, I don't think you can say she "broke her promise", just that she hasn't called you back.

In this hobby, many statements and/or promises are often not to be taken literally.  So don’t take offense.  About flaky ladies, I sympathized with you since I just gone through a similar experience with a DDG lady who promise to respond but never did. After back channeling (b/c) some of my fellow hobbyist I found this was a typical problem with this one lady and not a reflection of me.  I just gave up and moved on.  Interestedly, when she found I b/c about her she got very defensive.  I guess for some ladies good hobby etiquette means it is alright for them to be unreliable and to be able to screen us but not for us to screen them.

The unfortunate reality is that many providers -- and I don't mean all, there are clear exceptions -- live in the moment; neither past nor future has much tangible reality to them.  Hence, they have a great session, and tell you to come back for more -- on them.  The next day, that promise simply isn't real to them.  They're on to the next moment.    

The ability to live so completely and totally in the moment is a great occupational asset for them for obvious reasons.  But it has its downsides, too.

Why am I thinking of the escort who had 400 pairs of shoes, but was late on her rent?