While we will all struggle to get over the disappointment that was the lack of info from Nick Upfront 2013. Things like this always help.
We know of many new Book 2 characters from SDCC 2012, but 1 was not named. That being Unalaq's (Korra's uncle) daughters name, we know her twin brother is named Desna.
Now thanks to Bryan on tumblr
, we know her name is Eska.
This means that Alyson Stoner who we know will voice a character called Opal is not actually Korra's cousin. This more than likely means she will voice a book 3 character, though that is not confirmed.