Natasha was steaming with anger, walking in circles, sniffing the air, wanting, wishing that the female Auror would reappear. Didn't she have manors enough to know you didn't run from a fight? You died that's what you did!
She was still frustrated when Fenrir nudged her, but that didn't stop her from doing what he wished. As he broke into a run, she followed, hoping she'd find a way to get the frustration out of her before the night died and left her human again.