I have no experience of drugs persoanlly, but it would seem that once a person (whether they be male or female, black or white, working class or upper calss) has started to use heroin, then all they can see is heroin and can look no furthur than their next fix. It tears families apart. We don't know all the past history of these girls but their families may have tried everything they could and everything within their power to put an end to their childs drug habit - to no avail! Turning to prostitutuion is really the only option to assist funding their habit - they couldn't hold down a job in an office! So it goes from bad to worse. The drug changes their brain in a physical way too, do thinking changes, speech becomes dull and slurred and the sense of perception goes out of the window.
For all we know these families may have been to hell and back trying to stop the drug usage but at the end of the day, you can't change what you don't acknowledge and maybe whatever help was offered was kicked back again and again.