Put on the Snowcamo and dessert facepaint and lay down on the floor, she won't notice you that easy and comes confused, then when you have the chance take any gun (silencer recomended, so that you don't give away your curent spot) and ; when she engage you in CQC keep on tapping the circle button.
If she gets down on the floor take that opertunity and shoot her in the head or body, then you have to be carefull and run away, because when she gets up she starts shooting (best is to get behind a tree and press yourself against it so that she doesn't notice you.
(keep repeating this and it should be an easy victory)