Dear gma:
I am sure you have gotten a lot of good advice from the people who responded to your post, but I would like to add my two cents anyway. Of all the options available to your family, the worst thing you can do (I believe) is nothing. Whether your response is active (punishment, escalating if the offenses escalate), or passive (talking about it with, and in front of, the girl), there needs to be a response.
We had a teenage daughter some time back who started going down that path. She had some "problems", primarily a tendency to be overweight which affected her self esteem, so we handled her with kid gloves (as they say) because we didn't want to hurt her any more. We allowed her to get away with many things we knew were wrong out of love (we thought), since they were not major (no drugs, no sex, no criminal activity).
Unfortunately, our troubled teenager grew up to be a troubled adult. She is 29 now, and still has the same self esteem issues she had as a teen. She cannot have adult relationships, and she still relies on us for everything. We pray for her constantly, and she has made a lot of progress toward maturity. But there is no doubt in my mind that our laxness when she was younger contributed greatly to her problems today.
So my personal advice would be do something! In addition to praying for her (which I'm sure you already do), she needs to know that her family loves her and cares enough to get involved in her life, even if she doesn't want that right now.
Thanks for listening. God bless you all.

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This is the day the Lord has made. We will rejoice and be glad in it. (Psalm 118:24)