Books about horses I have read:
Pony Pals (It's for kids younger than 14 though). This series had a huge impact on me- I wanted to be the pony pals so me and two other girls on my street started calling ourselves the pony pals. My parents, grandparents and I still call my best friend "Pam" (one of the characters from the books) and her and her family still call me "Lulu". Her dad even forgot my real name when we were little... he was like "What is Lulu's real name?" because that's all he ever heard his daughter call me! Weird, I know, but we were the "Pony Pals" for so long that we just never stopped calling each other by those nick names!
Heartland I haven't read these books in a while but I remember absolutely loving them. They are centered around a girl who has lost her mother. They rescue and rehabilitate horses at "Heartland". Would probably be perfect for a 14 y/o.... I might reread them myself!
Thoroughbred I didn't read all of these books (there are a ton, and I read very few) but they are pretty good books about a farm that trains, breeds and races TBs.
Horse Diaries I believe I only read one of these books and I think it was written from the horse's point of view.
The Saddle Club I really liked these books! Similar to the Pony Pals, but for an older age level, and uses more advanced horse terms. There are a bunch in the series.
Canterwood Crest I read all the books in the series where Sasha is the main character and some of the books where Lauren is the main character. It's about girls who go to boarding school with their horses. The horse part of the stories are good, but I never liked that they are 12 years old and basically act like little adults. It always struck me as shallow or something.
Phantom Stallion (And also, Phantom Stallion: Wild Horse Island) I read some of this series, couldn't tell you a lot about it off the top of my head.
Hope Rising True stories about a horse rescue that also helps children.... amazing stories in this book!
Winnie The Horse Gentler I loved these books so much as a kid!
Horseshoe Trilogies I don't think I read all the books in this series. All I really remember is that the girl's mom was having to sell the farm and horses.
Animal Ark These books are about a vets daughter and not all of them are about horses, but some do center around horses and ponies. I loved these books because I have always wanted to work in the veterinary field.
Black Beauty Obviously, this is a classic and can be read by any horse lover!
A Horse Of Her Own This isn't a series and I don't remember a whole lot about it, but I do remember really liking it and I probably read it somewhere between 14-16.
I'm a huge reader and I'm sure there are more that I've read, but here are some! And there are other educational ones that I can provide you a title of, as well!
Journey, Spirit and Goldie... Love
is when reality
than your dreams