How old is this one girl? Personally, if I were you, I'd just ask her up front exactly what you are asking us. Explain to her that if she'd like to know more, you're happy to teach her, but it will take more effort on her part. If you're worried about pressuring her, approach it from a less confrontational direction (i.e. "You know, if you ever want to take your passion for horses to the next level, let me know, okay? I'm happy to help.") If she wants to do it, she'll let you know. Whether it ends up being a phase or not is up to her, and that's something you'll never know, especially not when she's in her teens. We all develop and change constantly. But at least you can be satisfied knowing that regardless of the direction her life takes, you shared your wealth of horse knowledge with somebody who cared (even if it's just that she cared at the time. Still, it mattered to her then) and you offered her an opportunity to take a closer look into a world that not many have the chance to experience :) ...Besides, sometimes, going to the next level is what teaches us whether we're cut out to be cowgirls/boys or not. But she'll never know if she's never offered the opportunity!