That sounds like fun. I've hidden from my dogs and they love to "find" me but I haven't tried it the other way around. :)
You need to start by deciding what you want the sound "hide!" to mean to her. What do you mean, specifially, by "hide"? Just "move out of my sight"? Or is it OTHER people you want her to hide from? Is this just a fun trick?
I would have no idea how to do that :)
But it sounds fun. So good luck!