Mr. Remington brought up some good points and gave you some good suggestions. How far are the other dogs from you when you're in class? If possible, move as far from them as you can, give your girl as much space as you can from the other dogs, and see if it makes any difference. That she's shaking and trying to hide tells me that she's just not comfortable in that class - be it the other dogs, the trainer, or all of it. When dogs are stressed/anxious, they won't eat, no matter how good the treat. When you call this a "behavior and training class", what are you learning in it? And is it positive reinforcement based? I find it unsettling that your instructor hasn't suggested that she's uncomfortable and that she may need to step back from the rest of the class, have more space and time, and do simple exercises (like practicing being calm in the class). Practice "watch me" at home (with her giving you good eye contact) a lot, so that when you get to class (and she's got space from the other dogs), you can ask her to "watch me" (you) and it will be something she'll do quickly. Some good eye contact with you will hopefully be the thing that will then help relax her if/when she gets nervous - but it needs to be a behavior that she learns and defaults to.