Just explain to them how you're both on different levels when she does drugs. The same thing happened to me and after hearing how most of my friends were bothered by it I stopped. Ask her to not do it at all, or at least whenever you're around her. If she doesn't want to hang out with you as much after that, well tough, she wasn't a good friend to start with then.
Worst thing you can do though, is spread this out and tell people that she is on drugs.
Worst thing you can do though, is spread this out and tell people that she is on drugs.