AFAIK only JSA is affected by your willingness to work, at least for single mothers. But as she's not claiming JSA, then she can chose not to work for as long as she likes.
The problem here is not the woman herself, as she's quite right - she shouldn't be in a situation where if she chooses to go back to work, it makes her worse off.
While it is true that all work will pay (and I really hope IDS's reforms deliver that), do we actually want to force women with pre-school children into work? Isn't it actually better for them to be looking after their kids?