Game of Thrones has both cast, and renamed, Theon Greyjoy’s sister, Asha.
To avoid confusion with the character of Osha, this sibling will be called Yara Greyjoy on season two, and she'll be portrayed by Gemma Whelan (Gulliver's Travels, The Wolfman). Yara commands her own ship and leads men into battle. She also has a thing for axes.
In other recent Game of Thrones casting news: