"cope as best she can" 
I sincerely hope that you don't actually work with families ravaged by drug problems!
"drug users are not bad people, just very often sad or mad"
You are so clueless that it would be funny if it weren't so sad.
I have lived in three cities over two continents and rarely met anyone who has never tried any drug, including successful business people and health freaks training for a marathon. For the most part, people of my age have tried at least cannabis, and usually cannabis, ecstasy, and cocaine. We then settled down, developed a taste for dinner parties with wine instead of all-night partying with drugs.
At no point was any of this sad nor are any of us mad
It was a lot of fun. Much more fun than alcohol.
If you don't even realize that drugs remain recreational for the vast majority of users, you are curiously uninformed in your field. If you have nothing to say to parents other than "You should have managed to keep DC away from drugs", frankly, you are useless and should considered a career change, for the good of those poor people you are supposed to be helping.