I would think there is no harm in mentioning you saw the picture and story on whatever the name of the publication is. I mean, you just saw it coincidentally. I'm not sure "congratulate" is quite the word I'd use though. It isn't like she actually won an award exactly. Those types of recognitions generally are not actual awards unless it is a tradition award given every year to the best volunteer. Even then it is really more about recognition and thanks than winning anything. (My perspective comes from being in the education business). Maybe just something like "That was a great picture of your family. Sounds like you've spent a lot of time volunteering at you son's school. Pretty impressive." I don't think she would have any problem with that and would enjoy the compliment.