The Maggie series does not have a new book coming out soon. The latest book, Maggie and Devildust-Ridin' High! (Book 3), was published in December 1990.
The first book in the Maggie series, Maggie and a Horse Named Devildust, was published in February 1989.
The Maggie series primarily falls into the Western and Historical genres. This middle grade series was written for ages 8-12, but can be enjoyed by older readers as well.