You're right, they couldn't hold her, but for the life of me, I do not know why they didn't keep her under constant surveillance until they could legally bring her back in. They had to know at that point even that she was, at the very least, going to be a person of interest in the murder of MW, and likely, the actual killer. Surely it must have dawned on someone in APD that she might not just sit around, waiting for them to come back and get her, after that initial questioning and release. I am not bashing APD, but in hindsight, letting her go free without keeping a close watch over her was a huge mistake!