Sounds like you've already had a vet check, but might it be a good idea to quarantine her for a few days as you don't know where she's come from? Obviously she's already been around your horses, but it might be a good idea.
Thanks, all! My boys are taking to her as if they've known her all their life!
I have no clue if she is broke, but i've been doing some groundwork and lunging, and she is a very quick learner (or mebbe she's had theses lessons before?) Anyway, I don't think she could've jumped, because the pasture we found her in is made up of calf pannels, and unless she's the next great steeplechaser, I doubt she jumped. Yeah, Im currently looking for missing horses, and I have put up a 'found horse' sign on windows of local convenient stores and grocers.