That's cute. I don't know how well her hand control is, but you should take her to an art supply store and let her pick out some nice supplies and paper.
If she doesn't have some already, decent paint brushes in several sizes (especially smaller ones) might really help her.
You could check your local library for very simple beginner painting books. She may pick up a few tips that can help her.
At that age I already had a collection of brushes, sable and synthetic, a lot of paints, and had been painting ceramics for nearly five years. I was lucky to have a very artistic uncle who encouraged me and bought me supplies - my parents wouldn't.