It's a classic play taken from her personal "He's really a simp" play book.
She cancels on you, then calls you the asshole for not fixing her problem. You were correct to decline to delay your date to accommodate her poor time- (and presumably dick-) management. Even if she was not seeing any other SD's or even civilian dates/hookups, her behavior has been disrespectful from day 1. She's treating you like an ATM instead of a generous older guy that she dates. Terrible foundation for a lasting dating (even if compensated) relationship.
So totally proper to call her out for bad behavior and ask her to correct it immediately. And the more she balks at your "guidance" and the less she acknowledges her poor behavior, the more reason you have to terminate the arrangement.
But do you burn it all down, or just turn away for better opportunities? For me, I'd have to think about how much I enjoy going BCD for the current allowance. I'd also want to consider if she is really trying to scam me or is just a sloppy hot mess who can't manager her way out of her panties.
No question that if she is trying to steal or scam, get out the flamethrower and go scorched earth. But if she's just careless and lacks an understanding of good/professional behavior, and if the sex is better than good, then perhaps pick from a less destructive path:
1. Tell her you need a break and will contact her again in the near future, but for now, it's off, or
2. Schedule less often, like go from 3x a month to 1x. When she asks why, just tell her you are busy. Let her fill in the blanks on WHY you are busy, and she will assume the worst, or.
3. Have a frank discussion with her, preferably by phone, but by text if needed: You need consistency and reliability. If you cannot rely on your date to meet when agreed, you will look for other dates. (Note: this is carefully worded about what YOU will do. It avoids telling her to change. Just like money questions are always about your budget and not her worth, you can only control your behavior, not hers. Let he decide that she needs to change on her own if she expects to date you in the future.)
For me, I see no upside in busting her about her activity with other SD's. It will likely tip her off that you and he are talking to each other. And that will likely make her behavior even worse. She may now try to play you two against each other, or she may try to ask for more allowance to get "preferential" scheduling. Ultimately, you will just be teaching her how to do a better job of behaving poorly by pointing out where she fucked up.
Please let us know what you decide.
Life is good
The Cat