In this I like to state that defeat is a state of mind. It is your perception that yopu can not solve this problem - here lies the defeat. Please don't be dishartened. Please don't loose patience. Marriage is a friendship between two souls. in this relationship of friendliness, there is no question of give and take. Please try to undertand that you wife was not mentally unstable when she was born. This society where you and your wife belongs, has made her mentally unstable.
I saw a movie where the wife is mentally unstable and even tried to kill her husband. But the husband with his love and affection helped the lady ( her wife) to come out of mental trauma and then the lady became quite normal. So far, I can remember, the name of the movie is"Chahhat".
I am certain your wife will be normal with your love and affection. only you will have to show little bit more perseverance.
Please try to admit it your failure if you can not convince your wife to go to a doctor. try to find out your shortcomings in failing to convince your wife.