She is not a kindergarten schoolteacher. She is not a grown woman.
She is a young girl.
This live show is an adaptation of the stage musical version of "The Wiz", not the feature film adaptation. As such, the production announced today that it is staging a talent search to find an undiscovered _young girl_ to play Dorothy.
The musical's official synopsis places her at "about 14", L. Frank Baum said she was 11. Diana Ross and the people at Universal in 1977 thought they could get away with Dorothy being "24". They thought wrong.
Mya is too old. Diana Ross was _far_ too old, because Ross may have been 33, but in that picture she looked 43.