Poppy is positioned RIGHT outside of the clothes shop for when you all exit. Literally right outside, at the other end of the road.

EDIT: Now, here's a thought.

What if the Knights managed to persuade Little Sister Poppy to help them, instead of curing her? Curing her only makes her lose her invulnerability, the addiction to ADAM still stays, and you might want someone "on the inside" so to speak. If she loses her eye-glow then she will technically not be a Little Sister, and people will get suspicious of her if she wandered around the facility.