So sorry for this. D is really pleading for help and the good news is that you are there to catch her. This is great.
And she journaled the stuff!!! Another sub-conscious plea, in my opinion.
I want to caution you about xeroxing the journal. You have the info and can send the urine off for the testing. That will be good enough. Here is my thought on exposing the journal. First, she does need some place sacred to vent... even if she is putting it right in your face.... Second, if you let her know you read the journal she may get better at hiding it. Do you want to have to dig further than this to catch her?
I say that you have plenty of already exposed info to take to counselling. You have a means to "discover" this other drug abuse. It may be really sneaky and dishonest and that may be why you would not want to handle it the way I suggest. But she has been sneaky with you and your sneakiness might just be to her benefit.. My suggestion? Use the info from having found her journal without her knowing that you read it. Sit on your cookie, there is plenty of time to let her know what you know...
Let her have her journal to work out her own thoughts.
Hmm. The counterargument... It may just be a great relief for all of you to have it all out on the table.