@Stokes what a lucky granddaughter! Unfortunately, I don't have a great answer for you just yet but have asked a few other folks and am hoping to have at least 1 recommendation for you soon. Most of our Family Friendly REI Adventures trips are offered for families with kids aged 8-17. More to come!
@Stokes after checking with a few folks, it doesn't seem that we have a trip that would be ideal for a 5 year old; most of our family-friendly REI Adventures trips are suited for kids between 8-17. I have 2 ideas: (1) you could call our Adventures team (800-622-2236) and inquire if any exceptions could be made if you booked a private departure. (2) although not the same as a week-long trip with your granddaughter, depending on where you live, there might be a weekend option, like a camping trip, or a day class, like Learn to Ride a Bike, that she would enjoy. I'm sorry we don't have exactly what you're looking for but hope these suggestions may inspire some summer fun!