Barefoot Helen and the Giants by Andy Jones

Helen is a fine hand with a slingshot, and more than at home in the woods. After all, she was raised by bears. When she stumbles upon three evil giants, she hatches the perfect plan to rid the land of them. Well, almost perfect...

Bulleybummus, the fiercest giant, catches her and insists she help kidnap the princess Antoinette. Instead, Helen manages to save the sleeping princess and finish off the giant before heading quietly back home. No one knows who the giant killer is, but Antoinette is determined to find out and comes up with a plan of her own.