I didn't realize that she hadn't actually *said* anything until I went back and read it. Maybe because she's pre-verbal right now "in real life," I just gave her a physical, nonverbal way for her to communicate in this "memory".

Yes, I think she'd be between 5 and 7 here. Not sure how old a child would be before building a sand castle might be too young of an activity. We went to the beach rarely when I was a kid, so I don't have any personal experience to gauge it by. But if we're letting her play on her own, within our sight, she'd have to be in school at the very least. And, she can dress herself . . . have no idea when kids can do that.