Lionsgate announced today that Michelle Forbes has been cast as Lt. Jackson in Mockingjay Part 2. This casting has been rumored for a few weeks so it's good to get the confirmation.
Forbes has done tons of tv work. You may recognize her from True Blood, The Killing, Chicago Fire and Orphan Black among others.
For those a little rusty on their Mockingjay (time to re-read!) Jackson is a soldier from District 13 and Boggs' second in command. She's a member of Star Squad who is an ace sharpshooter and she's also the one who comes up with the "real or not real" game to help Peeta.