This is a very tough question.
there are so many questions within the question...
- how old is she?
- what are the drugs she is taking?
- what control does she have over the father?
- what is your relationship like with the daughter?
so on and so on, i think at this stage you should write down the things you feel needs to change (for yourself to see no one else) and put them in order of priority, asking her to stop bringing her BF round, stop the drugs, go to school etc etc will make her rebel more, take each step at a time. what is the main problem?
try to talk more with the daughter and father, and i mean talk! not moan, shout, argue etc talk. in a calm manner try to put across your feelings, and if they respond with reasons for their actions listen, no matter how silly you think their reason are listen....
and once you can start to explain and communicate your feelings and emotions correctly this will be an amazing start.
i have a strong feeling your house does not communicate, that one person enters the other leaves, you will not improve anything like this, or by argueing.
it sound like their are a lot of underlying symtoms to why
- why she is taking drugs
- why she won't go to school
- why she will not listen to you
untill you can understand these and start talking, then the problem will never improve.
good luck