Think a little bigger, Dad. Take an international bus, Nicabus, down to Canas in Costa Rica. Cross the border in Penas Blancas on the way. Spend the night in Canas, take a bus to Cano Negro the next day and spend at least one night in Cano Negro. It is one of the premier wildlife viewing areas in the western hemisphere. Hotel del Campo is right on the laguna and the bus will drop you off at their door. You can take a boat tour early the next morning and see the laguna. Take the bus to Los Chiles, check to see if you can charter a boat from Cano Negro to Los Chiles – great river trip, and take a boat back up to San Carlos, Nicaragua. This puts you at the bottom of the lake. The river trip is always great and the view of San Carlos as you come out of the jungle is magic. Step out and take a boat to El Castillo the next day and experience the river. You can go all the way to Greytown and fly back. You can also visit the islands. You can take the ferry back to Granada or go around the lake by bus. http://www.thebusschedule.com has bus information. You can also fly back from San Carlos. A web site called the rightside guide has boat information and schedules.
This will renew her visa for 90 days and give you both a trip to remember so you can tell you grandchildren. Put some adventure into the trip. Think big!