Artist's comment:

"Though while she is still an Earth Pony, her fascination of the Pegasi and Unicorn magic have lead her to attain certain magical abilities and prowess of her own. Now the apprentice to a certain alicorn, she is gifted with her teacher's old spellbook to help her master the potential of her new powers."

An idea I recently had if the new Gen 5 were Dnd classes. It seems like an odd class for an Earth Pony, but with Sunny's story from the movie, it would make some sense to be a Wizard class. (Another alt to this could be the Warlock depending on how Sunny would attain her magic powers.)