Women are over-represented among walking commuters about as often as they are under-represented. This chart shows that relationship for 76 cities in all 50 states.
Unlike bicycling, data suggests there is not as extreme of a difference in rates of walking between men and women. However, research suggests that women often respond more significantly to improvements in street safety and walkable infrastructure -- both in walking more when such improvements are put in place, and in refraining from walking when safe environments are more absent.