Based on the most recent episode of My Little Pony: Friendship is Magic
*UPDATE: Added the Doctor's cutie mark.
*ANOTHER UPDATE: For the record I know that her cannon name is Derpy in fact I actually prefer to call her Derpy. It's just that this comic is slightly based on the "Doctor Whooves and Assistant" fan audio series on Youtube and in that series Doctor Whooves refers to Derpy as Dizty.
Also this got featured on Equestria Daily!: [link]