The famous Alyson Stoner, well known for her roles with Disney & Nickelodeon, has confirmed she will be the voice actor for a character named Opal in future episodes of Legend of Korra.
Stoner confirmed this role, as well as her other projects for 2013, on her official website.
However, she has not confirmed, as of yet, if she will play this role in Book 2 or a later Book. Looks like we'll have to wait to find out.
Uncle Iroh, being the wise man he is, sums up very precisely on how he feels about Book 2 in this meme/picture.