“No, no, no. You are under house arrest when state troopers park their car outside your house, without any authority to detain you, and do nothing to stop you when you decide to leave the house. Or something.”
Cops do not prevent crimes, they document illegal activity, then testify in court.
But cops arrest. So, if she was in any way legally required to remain in the house, they could have arrested her when she did. Instead of, y’know, doing nothing.