This is exactly the train of thought I think is incorrect: Businesses that can't pay workers a living wage should have to shut down. Workers (as a collective, and in the long run - not individuals in the short term obviously) are better off.
The idea is that businesses should compete on efficiency, not lower wages. When a business that can't pay a living wage closes, another can take its place that hopefully can.
> she combines this with her husband's income
This is another reason for having living wages: this persons low wage makes her economically dependent on another person. This might be a happy marriage but what about all marriages that aren't? Living wages means people can leave destructive and abusive relationships too.