IMDB.com is listing Sienna as attached to star in a new movie, The Trials of Cate McCullough. Kate Beckinsale is also attached to star, with Karen Concrieff to direct. The synopsis reads:

A former hotshot lawyer, now in recovery and estranged from her family, in order to be reinstated at the bar and recover custody of her daughter, must take on the appeal of a woman wrongfully convicted of murder.

We’ll keep you updated on any further developments/confirmation!