Lucie,
I think your instincts will tell you whether you should hang out with her or not. Confronting her will only back her into a corner and she will most likely get annoyed and it will not solve anything.
Her actions will tell yiou if she is okay to hang with or not. You'll be able to tell is she is using or not.
If she is maybe you could tell her that it is not the best idea for you to hang out with her when she is using because it makes you feel uncomfortable and she is not fun when she is like that, and it just hurts you to see her that way.
Others will be along to talk to you some more.
Hugs.............Lo