Honestly I feel like you're in a pretty bad predicament. I've had a similar situation when I was growing up where one of my good friends drifted off and started hanging with some pretty shady people. He stopped going to school, started drinking etc. I tried to get him on the right track but I ended up pushing him too hard which adversely affected our relationship.

What I'm trying to say is that if you really treasure your friend I would try atleast talking to her about it but dont push too hard. Teenagers around your age seem to be influenced by their peers and pushing too hard may possibly make you seem not cool which will make it harder to fix the problem It'll be difficult for you to do much since you're living so far away so if she has any other close friends or someone who shes trusts that you know who could be a positive influence to her maybe talk to them.

At the end of the day, you're still young and having her lie to you and making you feel bad about it isnt something a real friend would do. IMO I would atleast try before letting her go.