My youngest daughter also loves drawing. In fact, she grew a great picture of Jesus yesterday while at church!
One book series that she loves is the Dover "How To Draw" series. We have several of the books, and she refers to them often. Since you like horses, here's a link to "How to Draw Horses
" on Amazon.
But one of the things I recommend is practice, practice, practice! Practice drawing every day, and you'll gradually get better and better. You may even develop your own techniques, and someday be able to teach that to students!