Why not feed on the badguys?
So Sadie Blake needs to feed in order to sustain herself so she can accomplish her mission (to kill the vampires so that no more innocent people will have to suffer what she went through), but then instead of feeding on the bad guys to sate her hunger, she goes after innocent people? Isn't that exactly what she was trying to stop from happening?
I can understand her feeding on the dying homeless guy. He was innocent, but she was out of it and hadn't had time to get her new urges under control. But then why does she kill the innocent hitchhiker? Couldn't she have drained the blood of the 3 bad guys she'd killed prior? Or if she can't drink vampire blood, why not at least go to the blood bank, or kill some farm animals, or at least find some genuinely bad people (e.g. gangsters, corrupt politicians, etc.)? Just because the hitchhiker smokes weed that's not a reason to kill him. He's still someone's son/brother/bestfriend/etc.
And then she gets kidnapped by Bishop's goon at the bar, but she just lets him go with a broken leg and doesn't feed on him either. Is smoking pot worse than kidnapping? If she's got to feed on a human, wouldn't it be better to feed on someone who preys on the innocent and is a danger to the public?