The way i did it was, go to the chapter 1-2 on Veteran. Equip with 8 Health Sprays and a pistol, and take everything from Sheva. You should see a transformer on the ground to the left of your starting position, stay behind it and then call Sheva, when she is next to the trasformer shot it, then when she is leaving shot it again, continue doing this until her health is in the orange, then call her and restore her health. Repeat this 9 more times and you should have the achievement.