I don't see anything wrong with what she wrote.
I've done the same when selling something on kijiji, too many people out there seeking penpals nowadays and not the "x" they're inquiring about.
I can see you POV as you ASSUMED it...
But from hers [a business], if she has two subjects that want to be there for 1pm, and the first is stringing along, well, she's going to confirm out of COURTESY with the first to get in touch [dibs rule I suppose], to see if they are committing 100%, if not she'll go with the second subject for said time....
Just like selling. You get two replies 10min apart, the first can't seem to confirm, you bet your ASS I'm going to drop you for not confirming and going with buyer #2. First cum, first served.