This also happened to me when I brought Ice home, although he was nowhere near a weight that needed to be rescued, he did need to put on some pounds. It seemed that as he settled in to his new home he got nastier and nastier, when I bought him under the assumption that he was a giant lap dog. We moved him around between turn out herds and finally separated him completely (something you should do if you can still her attitude shapes up). The nasty attitude seemed to stop after a few days ago, when he tried to bite my BO and she really served it to him. Essentially she threw a fit, screaming "NO" flailing the lead rope in his direction to get him to back up, and she did this for about ten or so feet. When she was done Ice was stark still with a look of "holy crap". He tried to be pissy a few times after that, but he got the same reaction until he wasn't so nasty anymore.
It sounds to me like your horse got a little bit of weight on her and went from "survival mode" where she sucked up to anyone with her sweet attitude for food, to "test mode" and now she's trying to figure out her place in the herd. Aaand it sounds to me like she's kicking everyones butt. She may not need groundwork, just an attitude adjustment. Teach Your Horse to Respect Your Personal Space
I personally have not used this article, but Horse and Rider does have an excellent series of them, written by Clinton Anderson, and they have been on topics like proper leading, respecting space, and other issues that can be resolved from the ground.
It will take five minutes for you to assert yourself and say "HEY, you need to listen to ME", and as long as anyone who takes care of her uses the same techniques and doesn't let her get away with things, she should turn back into that sweet horse that you bought.