I think it is a great idea, I think that she will really appreciate it. I know I would, and the letter accompanying it will speak volumes, it will show that you didn't just see she is 20 years sober, but it will explain the gift and I know that I would read that letter with the gift and give you a HUGE hug and really appreciate it beyond words.
Recovery brings a lot of people together, people lean on each other and learn from each other.