Nic, luckily you sister is in a job where she will get support, they stick together through thick or thin. Bad as it is it would be so much worse if she didn't have family or workplace support.
In most states they have zero tolerance and police have no discretion but to act in cases of domestic violence (and so they should).
I hope the Sargent made it clear that he will be removed if it persists.
All the best mate, really hope it works out for your sister.