It's true, she indicated that her daughter has mental issues and did not indicate she has a mental illness but what else would you call it. She quit school because of these mental issues, has been seeing a doctor for four years, has been on prescribed medication and has experimented with other forms of non-legal medication. From my experience, I would guess that she has a mental illness and yes, her father is enabling her and not helping.
For the mother to leave the home and desert her husband is not a good thing. If the daughter is ill, which I assume given what was mentioned, she needs the support of both parents. If no real illness exists, then she needs to get out on her own.
James