Well, here you go! I hope it's all right! I don't have much experience with these sorts of characters, but I think she turned out fun.
Name: Katherine Sanders.
Backstory: Katherine is a young, but accomplished psychologist. Her field of study, and life's passion, has always been human reconditioning. How to alter another person's personality. What changes them. What pokes and prods can slowly shift them over to being someone else entirely. But she never had any place to put her theories into practice. But then, a friend told her a rumor of a certain ranch in Oklahoma. And following up on the rumor, she discovered the remarkable Historia. And a place that could fulfill all of her dreams.
So she became a rancher, and started her careful study. She found the style that suits her. At first, Katherine seems to the new pony-girls like a great individual. She's kind, sympathetic, affectionate. She seems almost sad to see them locked up. Sometimes, she tells them she can try to get them out. They just need to cooperate with a few procedures first. She kills them with kindness. And then, perhaps when it's too late, she can break them utterly. Or maybe she'll let them think that's what they wanted all along. She likes to keep things interesting.