Does she have any interests that she would like to persue?
There is a multitude of night classes etc which would get her out and about - photography, dressmaking, golf lessons, a language, ballroom dancing...... just a few to spring to mind.
Equally there are many clubs although they are not exclusive to widow(er)s - Hillwalking, orienteering, Lion's Club.
Or how about volunteering for a charity. A friend of mine met a great bunch doing the soup run for Simon.
There are opportunities everywhere but I haven't heard of specific clubs for widowed people.