Well, I think it's about time for an update. We spent 2 days getting everything dialed in. It took us a day to confirm that she didn't like the bars and saddle that came on the bike, and another day for me to source all the necessary parts. Ended up finding a 38cm Specialized Expert Women's short/shallow bar, and even managed to track down a shop across town that stocked quill to threadless steerer adapters (didn't think that it would be this hard to find one around here). Then, following the suggestion of fellow forum members, we found an LBS with a very generous saddle return policy, and went out together and picked her up a saddle that matched her sit bone width. Got the bars and saddle installed and everything dialed in the way she liked it. Surprisingly, she requested toe cages on her pedals when I tried to give her regular ole platforms. She chose a more upright position than I'm personally used to. We talked about it and both agreed that it's a good place to start for now, and we can play around with some longer stems once she's more comfortable on the bike if she starts feeling like she wants to stretch out on the bike a bit more.
Yesterday, we went for our first ride. Again adhering to the collective wisdom of the forum, I let her set the pace and distance . We covered about 5 miles, but our average speed almost doubled. She didn't complain about discomfort at all, but more time and miles will tell if any further adjustments need to be made. We did hit a pretty rough patch of the trail we were on, and boy did she not like that. We talked about the options to make sections like that more tolerable, and she decided that she wanted to try cycling shorts! I've also finally tracked down an LBS that can get 650x25c and 650x28c tires for us, so that will likely happen at some point as well.
And now, for a couple of pictures

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Action shot from when she was riding up and down an empty street, getting used to the feel of the brakes:
Happy but tired after our ride. In our 10 years together, this is the first time she's ever let me take a picture of her with something resembling a smile. Methinks that's a good sign:
Hopefully we'll get another ride in tomorrow!