This achievement MUST be done in solo with the AI.
If you want this very quickly, load Sheva and yourself up with only healing items (buy spray cans if needed), then load Chapter 1-2 and shoot the transformer to the ground. Stand next to it and knife it to hurt yourself so she runs over and heals you. After she heals you, press to say "Thanks!" and her trust will go up. Repeat this until you get the achievement.