What do you say to an old friend that is in jail?

I recently found out that one of my friends is incarcerated (in jail) for her third drunk driving charge in one year. She is stuck in there until the middle of next month. We haven't been as close as we used to be due to her excessive drinking and other things revolving around her alcoholism. We haven't even spoken to each other since I called her on her birthday over 8 months ago. I want to write to her, but I have no idea what I can say because I do not really know who she is anymore. Any ideas would be great, thanks in advance!