White Cloud Station
The White Cloud Station books, written by Trudy Nicholson, follow the stories of Suzy, Lucy and Alexa, as well as their horses, originally wild - Ripple, Hope and Liquorice (Liqui).
Each character is very distinctive - Suzy, the gentle but firm rider with a serious horsehair allergy fits perfectly with Ripple, the curly-haired bay with a great jump and lots of heart. Lucy, though quiet, is very caring and works well with Hope, an easy-going chestnut pony who handles tremendous setbacks particularly well. Alexa, the loud one with a go-go-go riding style, originally can't work with fizzy Liquorice. She soon has to get to know her horse, and herself, to know where to go next.
Each book shapes the characters a little bit more - they learn as they grow up, like real riders would.
Like most books, you shouldn't trust everything you read. However, this series has a lot of real concepts and techniques, such as join-up (though Mike, at the start of the first book, works with 4 wild horses at once - don't try that at home).
All up, this is a very good book series. However, I wouldn't recommend it to anyone under 12 - some parts of some books may be too scary or upsetting. Also, parents of young children may not appreciate the common use of minor swears.