Single mothers are always so defensive about the way they raise their children. I bet there's black women in the hood right now with boyfriends in jail sitting there with 12 kids bragging to their friends about how great of a mother she is. Materially providing for your children is not all that's required. Her getting defensive about the way she treats her children is definitely an insecure and unhonest personality trait.
Obviously it's frowned upon to enter a relationship with your therapist, but that doesn't mean it's unhealthy 100% of the time. Zoom out, size things up, and ask yourself if you really want to commit to this woman. Don't half-ass it, for the kids sake.