Karle Dickerson has written one book under his own name, The Forgotten Filly, though this is loosely connected to the Joanna Campbell Thoroughbreds series, to which he contributed seven titles in the Thoroughbreds series - the series is nominally by Joanna Campbell, but has been written by a number of authors.
Finding the books : all are easy to find in the USA: The Forgotten Filly is easy to find in the UK, and the Thoroughbred titles can be a little trickier to track down than in their native USA, but are not impossible..
Sources and links:
Terri A. Wear: Horse Stories, an Annotated Bibilography, Scarecrow Press, 1987
National Library of Congress
Bibliography - horse books only
The Forgotten Filly
HarperCollins, New York, 1993
Hodder (Knight), London, 1994
“Joelle is thrilled that her favourite horse, Dancer is expecting a foal. But tragedy strikes when Dancer dies giving birth. Joelle's world falls apart. She blames the little foal for his mother’s death. She's convinced she can never love another horse. Finally her parents decide they had better sell the foal. Then something happens to change her mind forever...”