Let me ask some simple questions and I don't think there are any completely right or wrong answers. I won't go down the road of "tough love" because you can get that from lots of others very easily. I will say, they are not in your shoes at this moment, and neither am I.
Drinking and "smoking", will it have an immediate and irreversible impact on her life at this moment?
How you deal with this could have just such an impact on your R with her for at least some extended period. Try to avoid acting on emotion. That always bites us on the rear. Try to think "will my action save her life "today"? Or, "will my action today cause me to loose contact with one more person I love completely?" This is a bit of a fragile balancing act.
You are paying a C to talk to her and the IC is trained at being a constructive participant in this process. Let me promise you that your DD will listen better to a third party than you. It is what kids do. Oh yeah, as you know ... they lie to keep from hurting you with the truth. They lie to keep you from being angry at them. Good Kids sometimes lie for reasons they can only justify to themself.
Knowing she is not being honest hurts you. Finding out you snoop will hurt her more. Please accept that there are things in her writings that you should not be going to look at. I know you care. She knows. Now maybe you need to try to care and respect her expectation of privacy; by letting the online journal go.
You can change some things in life, and not others. You can't really change people, even if you are able to impede their behavior. Your DD is at an age she feels compelled to experiment just as 90+% of her peers are. Learning years. Like a MLCer. She is testing the waters of certain things in life and deciding which ones she will embrace, which ones she will reject. But usually only after fully experiencing the options. Not to mention the fact that there is some turmoil going on in her life when she should have the undivided love and attention of her dad.
It is what it is. So what I am saying is, you may find comfort in talking to your own IC about how to step back and let go as much as appropriate in this situation. Or schedule time with her IC after they meet. Just don't expect her IC to share everything with you. It would only be so her IC can help you accept what you may be unable to change immediately, and sort out what is not yours to change. Be strong, but be patient.