I can see how that would be a tough situation to try and get the point across - I was raised in a very sheltered, strictly drug- and scandal-free household and still grew to see drugs as no big thing because of the friends I hung out with - and most of them got their casual attitude towards drugs from their own parents, some of whom were dealers, or would buy for us, or would smoke with us etc...
And just to throw another spanner in your works, how long has she had the implant in? It pays to watch very carefully if she's got any emotional/depression issues or has a tendency towards emotional instability (and there's not many 16yo girls out there who don't fit that description...) - the Implanon can trigger depression and suicidal ideation, so keep a very close eye on that one. One physical sign to watch for is weight gain (mine was very rapid, people commented on it a lot), and try to continue being as open with her as you have been, watch for signs of emotional disurbance or depression (withdrawal, anger, acting out etc) and contact your GP if you have any concerns. x