I would totally acknowledge it with a warm congratulations. A card is nice, too. I always like a sentiment like, "I know how hard you've worked for this, and I'm very proud and happy for you." Keep it simple, not gushy.
I absolutely LOVED picking up my chips at 30, 60, and 90 days. I remember feeling sad when it then became 6 months, and a year, and then it is just the years that got counted. However, NOT sad enough to go back for another 30-day chip!
I'm proud of her, myself. It's a start, hopefully of a whole new life.