J.
Give her music lessons! This is something she may enjoy for a lifetime. 3-4 years old is the best time to start children on a string instrument or piano. I am a professional violinist, and I have alot of experience teaching children. The kids who start young have a much easier time. They are little sponges at this age, and nothing is hard for them. I would recommend the Suzuki method for string instruments. Something that involves both private and group lessons at this age works the best. Private lessons for individual attention to correct techique and group to motivate the child and to have fun.
J.