It sounds like it may be too late to me, like your friends are on to other places in their lives and the close relationship you all shared is now "missing" pieces of experience that can't be recovered (she's not sharing with you her love/relationship/experiences anymore). I had a couple good friends where a big, confusing argument/fight caused splits or where a change in their other relationships did. It's possible that even if you had not had the Vegas problems that she might have drifted away, since it sounds like her relationship is now changing her too?

I don't think it would hurt to call her, see what you can learn but I don't know that the relationship can ever be "fixed" so it's back the way it was.