I also don't think you did anything wrong. Something like that is bound to be a shock. On one hand it may be a good thing that she chose to tell you, as it may mean that she wants to be honest. My concern, in such a situation, would be whether she would relapse at a later date. Also, as hvert says, is she opening up, or warning you? My guess is that she wants to tell you more, but she is scared of the consequences and also feels ashamed. Perhaps the question is what caused her to develop that addition and what has changed to enable her to recover from it.