The vast majority of widowers don't turn to illegal activities to make ends meet. Selling drugs isn't a normal reaction to losing a husband. And from that I extrapolate that Nancy Botwin was never a normal person.
It's not a new idea on television to have single mothers do desperate things. But surely there are TV shows with strong women in a lead role. Yet no show in the top 5 or even the top 10 had a woman as the lead character, much less a single mother.