Okay, first off the only person you are responsible for is you. The minute you try to focus in any way on someone else in the house you are not working your program. I'm not trying to make you feel bad but you rejected her offer of the pills, the next thing you could have done is talk to someone about your fears of future drug use.
This girl you share a room with could be a future neighbor or co-worker. Will you have the tools to say no then? This girl will implode on her own. See how upset you've made yourself by giving her sobriety any thoughts? We all have our own paths, hers may be more messed up than yours so don't get sucked in.
Focus on you. Post here about your feelings some more. You're going through a ton. There are always users and liers in most sober living homes and they are always found out.