As reported at Winter is Coming, actress Gemma Whelan has reportedly been cast as "Yara Greyjoy", who, according to a casting breakdown, is the renamed Asha Greyjoy from the books, the sister of Theon Greyjoy. It's been speculated that the name change is due to the original name's similarity to Osha. Oh well.

Meanwhile, George R. R. Martin gives us another casting clue, just like he did back before the season 1 premiere:

I’m Blue
The she-wolf of France has stormed the barbican. The Aussie turned her into a bunny.

Sounds like a female character. Could it be about Gemma Whelan as "Yara" (as a fan of the books, I'm not sure if I'll get used to the rename)? Or someone else? I'm sure the fans will solve the riddle soon.