Hey WesternBella! I'd say the way to stand out as a writer is to write what you feel passionately... so take those aspects of being a teenage girl, loving horses, facing those gut-wrenching challenges, and put your own personal spin on them. That's what I did with my first book, and it worked out pretty well - it's on the USA Today list, it's gonna be made into a TV series, and the 2nd edition is about to come out :)
Good luck, and keep us posted!
Oh here's the link to my book if you're interested:
Whatever you think you can do or believe you can do, begin it. Action has magic, grace, and power in it. – Goethe