Well, after reading journal after journal, perusing maps and photos and Google Earth, and many phone discussions, we've finally selected a route for Mom's 60th Birthday Tour Extraordinaire. We will be doing the Adventure Cycling "Washington Parks" loop. It is actually a double loop, and we will be doing the smaller one at about 300 miles.
The loop encircles the Olympic Peninsula in Washington and has very little terrain, but lots of views and fun. We're even hoping to throw in a day trip by ferry to Victoria, since Rick and I missed that when we were in Canada in 2007.
Thanks to all who gave suggestions and advice.