You've tried and others have suggested a lot of what I do, so I don't have a lot to add, but here are a couple of thoughts. For the treats, try something soft and stinky, like chicken weiners. Pink just about went nuts when I brought out the turkey weiners. As for the in class breaks, if your instructors/class situation permit, try taking off at a fast run, cheering her on.
I've taken all of mine to school. There have been huge variations in how quickly they learn and how much they can handle at once. Several have hit a plateau or shut down for varying periods. Graham is currently on an extended (maybe permanent) break because he finds it all too stressful, even when practicing at home. He's got his basic skills, and he behaves well, so I've switched my attention to those who need and/or enjoy it more. I just do the occasional sit/down/whatever with him, and he's much happier.