L.D.
She must get him help. He is not in a place where he can get it himself. She needs to call a number, put him in the car, and drive him and walk him to the door. If she doesnt think he will go, she can even lie to him about where he is going. She can start with taking him to his primary doctor who can refer him to other places. He may be angry, or he may be grateful, but she needs to get him help.
If money is an issue, she can get him signed up at UT Southwestern. They have students there who work with people who need help/have mental illnesses. They are supervised by a doctor, and are probably more conscientous and attentive than a regular psycologist or psychiatrict who sees lots of patients. In addition, they can prescribe medications.
He probably needs more than vitamins and exercise by what you have described. Also - there are LOTS of medications for depression, so if one made him sick, there are others he can try.