In the Lady and the Cowboy, set in Texas circa 1882, I use a female jockey. I can say much more without spoiling parts of the book but I wanted to share my research with you.
First of all I wondered if women might be banned from the sport, after all, women were banned from many professions in the Victorian era. I could find nothing prohibiting it at that time, then I hit upon Eliza Carpenter, who was extraordinary for many reasons, not least of which is that she was a former slave turned racehorse owner, and she would ride her own horses when she was unhappy with her jockeys performance!
Sadly details of her life are few and far between, with everything online basically being copied from or to her brief Wikipedia entry.
I did however, find her obituary from the The Baltimore Afro-American (below the cut). Sadly she was thrown from wagon in 1924 and hit her head. She never recovered from the in injury and died a few months later.
She lived a long life however, being 73 at the time of her death and I think you will agree, she was a truly remarkable woman.
To reach chapter one of the Lady and the Cowboy, click here.