Hi ExhibGuy,
As a provider, I would like to thank you for addressing the situation in this public forum with such discretion. As soflaguy said, this is what the site is for.
I cannot speak for the lady in question as I don't know her side or situation, however, there is a reason and neither I nor you (nor anyone else BUT her- really) just don't know what it could be.
I would advise you contact her via email and let her know you were disappointed (that is if you still would like to see her). For many experienced hobbyists, this is a good way for a lady to LOSE business, ie. they won't try to see her again and will tell others of their "bad" experience (by posting her name as the "offender" on this site).
Please keep your gentlemanly manner in your communication with her and give her time to reply. You might want to pm her the link to this thread you started so she can read (as I read) your total confusion and see what a gentleman you are. Give her the option to just reply that she did receive your email and will answer in an allotted time (date/time) -for example, her reply could simply be:
Dear ExhibGuy,
I received your message concerning our previous plans. I will have time to reply by Monday, July 12th at 9 pm)
She may need some time to be able to organize her thoughts and respond. Be prepared to accept her reasoning.
If you want to see her, you should not allow frustration or disappointment in the "run-around" to be reflected in your communications with her. And by no means, continue to email her and call her if she does not answer. This can be considered "stalker-like" behavior and then you really will never get to see her and reflects on her good instincts at not seeing you for the appt. Right or wrong, this happens. However, should she fail to respond, it is at your discretion whether you will share the information of who she is publicly(here) or privately (via pm).
You say she's well-reviewed and a professional.
Something may have spooked her. Who knows??? With a little suave effort, you may find out and then, if "the stars align" and you want to try to see her again, start off fresh. If she's a pro, she'll make it up to you.
Heck, I've had my phone die and not have packed my charger, not have a car(travelling) with my car charger to my phone in it and missed out on business because I had to get a taxi, go to a few places (with the taxi meter running!) to find a charger for my phone only to find out I missed several calls for appointments but not to call them, they would call me back. And of course, when my phone had power, it didn't ring!
So, life (and in most cases, it's SHIT!) happens ... Luckily, there are plenty of fish in the sea (maybe not the Gulf, but that's another story entirely
)
Good luck on your quest(s?) 
xxx
Jinni