Sounds like she is getting overstimulated. Lucy has the same problem. We've done a LOT of focus work, getting her to keep her attention on me when other dogs are running (something that is very hard for her, especially on noisy obstacles like the frame). Basically, I just shoved cheese in her mouth whenever other dogs would run, and then gradually increased the time between treats.
Depending how much it bothers your classmates, you could also try crating her and covering it with a sheet (to block the visual) and giving her a bully stick or something to occupy her. Lucy still barks for the first half of class when I do that, but she's learning it doesn't get her anywhere--it's taken several months though. Not sure if you're willing to wait that long.