How does she feel about hills? If she doesn't like them that may limit your choices somewhat. The west coast of the U. S. has constant ups and downs. The San Juans all have major climbs up from the ferry dock - maybe not too long but plenty steep.

If hills are an issue, how about rail-trails? The ones in Northern Idaho around Lake Couer d' Alene (sp?) look very promising. There are others. The Katy Trail is something I'd like to try, but I've heard there are issues with mud or loose dirt. Comments anyone?