Even though I keep loaded autos for HD, revolvers would work as well. The thing about a revolver is with kids around I'd opt for a SA without a round in the chamber. The problem for a small person might be racking the slide on some pistols. That would have to be addressed.
A decent inexpensive 9mm (SD9VE) and some training and practice would be my suggestion. Shooting for center mass can be accomplished easily enough I think, but becoming proficient in the operation and handling of pistol would be where I'd spend the time practicing.....and making sure she has the ability to shoot someone if needed.