This can be one of the most frustrating parts about dating and game. As men, we are problem solvers, and we want to think we are in control of every situation - it's easier for us to think that we did something wrong that caused her to ghost us because that means it's something we can work to figure out and then fix so it doesn't keep happening with future women. But it isn't always our "fault" or anything we could have done differently - girls are very fickle and go silent for all kinds of reasons, some of which having nothing to do with us or anything we did. There lies the catch-22: To learn good game, it is a fact that a man must improve his skills with women, but how can he improve his skills when there is a high amount of randomness it male-female interactions and we never get any feedback from the woman who ghost?
I could list 1,000 reasons why a girl ghosts a guy, all of which have nothing to do with him. Her dog could have died. She might have a boyfriend and was just looking for attention and validation and before things got too serious her guilt caught up with her and she ejected. She could be talking to 10 different guys at the same time and decided to choose a different guy over you. She might have psychological disorders that cause her to isolate herself every few weeks. The list goes on and on.
As for learning game, the best thing to do is ask questions here, like you are now. Be as specific as possible and provide as much information as possible about the interactions and timings and we can look to see if anything stands out to us as glaringly obvious but from the example you gave, this doesn't sound like anything you did wrong. When you cancelled, you gave a valid reason and immediately rescheduled which is perfectly acceptable. When she said she wasn't going to make it and didn't offer a reschedule, that's soft-rejecting you. When a girl does that to me, I assume that's the end of it. I'll either not respond at all 95% of the time, or if I do respond I'll say, "Sounds good, we can just do it some other time" and that will be the last text she gets from me unless she asks ME for a date.
If you are worried that your date reschedule is the reason she ejected, DON'T BE. First of all, you didn't do anything wrong. Second, if this actually WAS the reason she ejected, then this is a blessing for you: You have successfully screened out a narcissistic, entitled princess. Imagine what that girl would be like in a relationship any time she doesn't get EXACTLY what she wanted? Or she is the extremely insecure and jealous type who always assumes the worst about you - and she automatically assumed your reschedule was because you had another date opportunity and you took it and lied to her about why. Imagine what dating a girl like that would look like? I've been there, I know, you don't want anything to do with it.
Bottom line: When this stuff happens, think of it as women screening themselves out - they are doing your work for you and making it easy for you.