It may well be they are aware of her but have been warned of by the drugs squad, who may be after the person who is supplying the woman.
This happened to me before we moved here - a couple of lads were dealing and one of the neighbours actually caught it on camera not to use in court but just to show the police what was happening and although they came a few times aroound the road they didn't approach the woman.
I can't remember everything that happened but another neighbour knew a local policeman who said they had been told to virtually ignore them as the drug squad had them as a target and they had priority,not sure if that is/was true but some 4 years later the 2 lads, and their dealer and another dealer have been charged.