My just turned five year old did fine with all day touring a few years ago. It was in early Sept, so just as hot too. I think that AK has plenty of indoor activities like the shows with air conditioning, etc. and your are doing two sit down meals. I would go with your plan and make the decision on the spot if you need a break. My gut tells me that you will be fine! The evening show is at 9pm, so it's not like she will be waiting for super late fireworks or anything.