It sounds like she does have symptoms of depression. I understand not being a "kid person" because I'm generally not, except with my own kids. I've stayed home with my kids for brief periods (maternity leave, summers off when I was a teacher), and it does not suit me. I need to work outside the home to be at my best for the kids.
How involved is the dad with child rearing? Does he seem to take a different approach, or follow her hands-off lead?
You mentioned that the son has therapy--do you know what type? (speech, occupational, etc.) Does the mother participate at all, and do they work on any behavior-related stuff?
Would she be open to taking a parenting class? Would the husband be on board, or could he encourage her to go?