Granted Fluttershy may have had a bad experience with dragons, but it would have to be something even more traumatic than just a bad dragon experience to create her persona. She is afraid of her own shadow, leafs startle her, becomes so timid she can't fly. I feel the writers made her too vulnerable, she is so vulnerable and seems so unwilling to not get help(or accept help) to become less vulnerable. And if there was something traumatic (which would be helpful if there was an episode but there is not so we got to guess to continue this) then I feel it would be her friends duty to help her get over it. (Friend of mine got robbed, and he was shook up so the first few days no one mentioned it, but eventually we got him to talk about it, and eventually he realized that he can't let this mishap stop him)
I agree with the stage fright analogy, it fits well. But, anykind of fright, any kind of emotional damage has the possability to be over came if person wants to, even just a little. Which I would hope most people (and FS) would. And if she wouldn't want to that would make her less likable, or at the very least make the effort to over come it.
In the end though, FS judged an entire group based on preconceptions, and prejudged them for it. She continuously judges all dragons (for whatever reason), and even though she knows nice dragons (spike, and Magnet), she still doesn't seem willing at all to give them a chance. Even if she has a reason (good or bad) to prejudge dragons, the fact remains that she (the element of kindness/ and animal whisperer) isn't giving them a chance.