She is transforming to Alicorn.
She read a book and did a magic spell. So she can move on to the next level of study and test.
The book from Luna.
Is anyone still remember a book from SS3 ep.2 where Luna took the book out from no where at the end?
Why did Luna take it out? and What is it for? I don't know d -.-b
EDIT: Okayyyyyy! After watched MLP-FIM S 3 Ep 13, Shit just got real. She turned into an Alicorn!!!!!! from that Book!!!!!!! WooHooooo~~~!