This kind of happened to me once. When she was at Kings Cross, had a confirmed time and date a couple of days before. Then on the day itself, nothing. No phone pick ups etc. Wasted about 30 mins.
When I emailed her through AW, she apologised as she said she had been sick but made up for it by offering me a knockdown price session next time, which I took her up on. And then we were back on an even keel.
Since then, no issues the 5 or so times I've seen her.