Walter Farley has a lot of books you can look at.
http://www.theblackstallion.com/books_theseries_n.htmlBut as far as a central female character - L'Engle's "A Wrinkle in Time" is good.
http://en.wikipedia.org/wiki/A_Wrinkle_in_TimeAll of her books have a GT undercurrent:
"Meg Murry is a teenage girl, regarded by her friends and teachers as a bad-tempered adolescent. Her family recognizes her problem as a lack of emotional maturity but also regards her as being capable of great things. The family includes her pretty scientist mother, her mysteriously missing scientist father, her five year-old brother Charles Wallace Murry �a nascent super-genius� and ten-year-old twins, athletic brothers Sandy and Dennys."