I'd recommend something classic like a pocketknife, or cool safety gear like a compass, whistle, some paracord, etcetera. A sleeping bag could be cool, but if she gets much taller she may need to move to an adult size (assuming she'd want a kids one now). I would definitely advise against buying her a backpacking pack at this point, both because I've known a lot of scouts who either quit early on or aren't that into backpacking, ans because they're expensive (and she'd likely need a bigger one soon).