Hi PS
I think its great if you communicate with your daughter & she really needs that.
From experience, (my sister was an alcoholic) my neice needed to know her mother was ok you know. she was about 17 when she left her home. I know that she would pick her up or try and meet her for small periods of time even if it was just coffee or shopping. sometimes I think it may have been more about spending time with her than actually talking to her on the phone/emails. My neice would tell me about the times they spent together but never really got into the nitties of it all. (I never asked either, as it was their time). Maybe your daughter will hopefully value your own relationship and not involve your sister. Dont worry too much about 'the right things to say.' Just love each other. How old is your daughter?
JJ