Is there any possible way that she got in the pasture by herself? Even jumped in? Horses will do that. I would post ads about "Horse Found" being vague about her description and see if anybody responds with a proper description of her. I also wouldn't announce that you spent a bunch of money on her or you will get a rep for saving other people's horses, then they come back to claim them and you're out the $.
Glad she found a good place to visit or move in to though!