Leah didn't smile at the compliment. "I did what I had to," she replied in a flat tone. Killing zombies was neither fun nor impressive. For her, it was a grim form of therapy. With the right person, she was willing to turn a battle with a horde into a game of who could kill the most, but that was about as far as she took it. It was a necessity, ridding the city of the undead.
Watching him take a drink, the woman briefly considered asking him about his wound; if he was bleeding or not. However, O'Brien was the chatty type, so if his shirt was stained with blood, no doubt he'd tell her. It should've been enough that she'd found his medicine, got him away from the zombies, given him water, and offered to get him back to a safehouse. What more could he expect from her? Nothing, that's what.
"You're right about that," she said, her attention returning to the street below. "If you hadn't shown up, I'd already be at City Hall by now." Turning, Leah took a seat on the roof's small wall, leaning forward and resting her forearms on her legs. It didn't exactly answer the question of why she'd decided to help him, but then, she hadn't really intended on giving him a straight answer for that question.
When he thanked her, she nodded once. "I don't leave people behind," she explained. "Unless they really deserve it. You didn't."
Leah stood up after a couple minutes, stretching, her gaze once again going to the sky. There were a few clouds, no doubt a sign that snow was on the way, but for the most part the sky was clear. The moon was bright, giving them enough light that Leah's flashlight wasn't necessary.
"You gonna pass out on me?" She asked, striding over to retrieve her bottle of water. "'Cause if you are," she said, straightening up and tucking the bottle back in her bag, "I'm leaving you here. I am not dragging your ass all the way back." Can't would've been a truthful word, too.