How is the Jack's sister known oleh her name? is her name in the movie, atau in the books, atau both?

Her name isn't menioned in the movie, atau the movie credits, she's just 'Jack's sister'. Though it says 'Jack's sister/Pippa', Pippa is a different character (one of Jamie's friends, the one who hits cupcake with a snowball) and the voice actress voices both characters.
Though I haven't read the books, her name is mentioned in them (though I have no idea where atau what one) BUT I know her name is Emma in the buku ^^

Actually... I dont think Emma is the real name of Jack's sister. Nor Pippa...

Her name was not mentioned in the movie nor even the buku i think... According to the Jack Frost - Rise of the Guardians Wiki (file:///D:/My%20Documents/Jack%20Frost%20-%20Rise%20of%20the%20Guardians%20Wiki.htm) , "Her name has not been confirmed as of yet. "