Why did I do this?

Twilight uses a spell on a book she found, when she explored the castle of the 2 pony sisters.

Twilight went to the castle of the 2 pony sisters and saw a book on one of the tables. As she saw the book she began to look on it's cover, the book was named, Advance Magic Spells, she kept it on her saddlebag, and started to dust the dirty bookshelves. Though when she went to back to the castle she saw a spell that was so dangerous but, did she know what she was doing?