I wouldn't worry too much, nick. She's probably just a little scared.
Here's a story from my work with massasaugas, but I'm pretty sure it'd be standard for most snakes. The snakes that we tracked everyday got pretty tolerant of human presence (at least mine and my boss's) and and they would just kinda chill while we took data, and as long as we didn't disturb them, most of them wouldn't even buzz. Well during the mating season we found a lot of new unmarked snakes with our marked snakes. The newer snakes were pretty freaked out by our presence, and would freeze as soon as they became aware of us. As our presence continued sometimes they would start breathing really heavily for a bit, and then take off (sometimes dragging the marked snake along behind if they were locked up). So, long story short, I'd guess its just a response to prepare them for "flight." There's probably nothing really wrong with your snake.