Turns out it was a "signing only" event. I'm not a big enough fan to pay for a hardcover version of something I'd already read most of, and apparently neither were most people. Half an hour before the 7:30 start time, nobody was lined up, there were only slightly more than the usual number of browsers in the store, and I saw no signs of a line. I don't think she canceled, because there was a sign outside the front door telling the crowd which wasn't there how they would be given a number, and at 7:30 they would start being called in by number.
So Plan B, which originally was put in place because I expected an overflow crowd to hear her speak, was to go back to the car, grab a book and book holder, and have dinner next door either at Cafe Baronne or the British Banker's Club. The BBC looked too dimly lit to read, and there was more eye candy per square inch at the Cafe, so I ordered a lasagna and iced tea (which happened to be the night's food plan meal), parked myself at a table in the corner with a good view of the front door and the ordering line, and split my attention between the book and the many attractive women coming in the door.