InvisiBelle

Sweetie Belle tries and fails to cast a spell, leaving her with some undesirable changes. She's very unhappy about this. Unfortunately for her, so is everypony else.

When a spell goes awry, the only pony who can help Sweetie Belle is nowhere to be seen. With an apple-crazy mare getting on her nerves, an angry mob chasing after her, and Fluttershy shutting her out, what else can she do? RUN!!

Story idea given to me by Fonypan.