Why would a mom knowingly deny her child medical care?

when she has health insurance and EVERY needed resource available and made known to her, at no cost to her? What would cause a mother to deny care, allow serious conditions (dental, hearing, speech) to worsen, and months of excruciating pain and trauma to develop in her child - and hide the pattern from the other parent? Is there a psychological condition that matches this scenario?
--------------------
She isn't being responsible for what ever reason. Take the power of decision making for the children out of her hands since she doesn't take it seriously. She is affecting another person's life.
Source