If you guys are into trains or could be I reaaly recommemnd the Whitepass and Yukon. It's a great train ride. (Skagway)
Glacier in Juneau. 6$ bus ride
Ketchican...Hmmmmmm maybe the logging show or whatever it's called a very short walk off the pier.
All three towns are easy walks to business. Skagway being the furthest maybe 5 mins. The others unless you tender are right off the dock. unless in Juneau you are positioned away round the harbour. (RCI I think)
I second the White pass trip. She may fall asleep however. Our son did.
Check out the Duck tour in Ketchikan. kids love it and for adults it's nice too. Goofy but a tour of the town and then it drives into the water. Get the souveneer duck call and she'll love it.
Duck tour in Ketchikan, and maybe the lumberjack show?
My daughter (6) loved the train, but the ride down was spent listening to her iPod.
Have you thought about taking her fishing? Juneau and Ketchikan have great shorter salmon fishing trips that - if you're careful which boat you select - are VERY kid friendly. Fishing is always the highlight of my outings with my kids, especially if they can catch a fish bigger than Mom or Dad's!