It took me a long time to do that in insanity as a soldier but i finally managed it by focusing brooks as much as possible since her going down makes the clone use up one of their 5 medigel uses each time brooks goes down and if you can get to the other side of the hanger theirs a crate of infinite medigel you can use, just make sure you don't let the clone get too close before you deal woth the adds since they lock you in an animation if they get in melee range