Because he was still just a boy. The way Nancy knew him.

She sobs, holding the body to her chest, rocking him softly. "It's okay, Oliver," she tells him softly. "It's alright, I'm here now, you got your Nance, an' Dodger's here too. We got you. See? I told you I wouldn't-" her voice cracks "wouldn't let anything bad happen to you-"

and she'd failed. Was this the result of what she'd seen at her arrival party? What she'd felt? The inevitable failure of her betrayal?