I sent a polite email that basically explained that if we didn't hear something by such and such a date, the ressie would have to be cancelled, and then we got a "sorry, I forgot" email with a promise of a tracking number soon. The tracking # didn't materialize on the promised date, so dh made a phone call. He was very nice, but firm, and she promised it by the next Friday. Never did find out exactly what the problem was (I'm thinking perhaps it was more an unforseen financial problem than a true forgetting problem maybe?). Anyway, I sent a reminder email on Thursday, and on Friday afternoon a tracking # came by email, then on the following Monday the money order arrived. So all's well that ends well in this case; it was just a bit of a hassle and somewhat worrisome & uncomfortable. I was SO glad not to be forced into any unpleasantness, and I'm grateful it all worked out just in the nick of time for us to take our little trip and thoroughly enjoy it. I think spelling out the consequences of late/missed payments could alleviate this in the future (hopefully), if we ever do this again.
I'd like to say thanks again for all of the helpful ideas and input from you guys.