She's running. She could let her. Shura knows she had stabbed her plenty o f times, one of those hits might have struck something important. Billie could just go on and bled out on her own. But that would be a crappy way to die, and even worse, she could not die! She could go on and get caught eating another corpse by someone who would be more troublesome to deal with in the long run than Shura.

So Shura takes a swing, letting out another blast of cold air. It's not as strong as it needs to be to finish Billie off; Shura just doesn't have that much strength left in her.