I am engaged to a young woman but soon after the betrothal she fell sick. Her family took her to see many doctors, but they said that she suffers from no disease.
I had some suspicions about her sickness, so I sought the help of a righteous friend and he diagnosed the cause of her sickness. He advised me to break off my engagement because she suffers from a very difficult Jinn possession case, which would cause me many troubles and embitter my life.
However, I performed Istikhaarah (prayer for guidance) and put my absolute trust in Allaah The Almighty and I decided not to leave her. I have heard about some Sharee‘ah-approved methods and other methods to treat such a case. What should I do, especially since her family objects to sending her to people who are experienced in the treatment of such cases?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

It is permissible for you to try and treat your fiancée through Sharee‘ah-approved Ruqyah, as it was narrated on the authority of Jaabir that the Prophet, sallallaahu ‘alayhi wa sallam , said that Allaah did not create an ailment without a cure. He, sallallaahu ‘alayhi wa sallam, added that when a proper remedy is applied and there is no impediment, the ailment is cured by the permission of Allaah The Almighty. [Muslim]

It was also narrated on the authority of Abu Hurayrah that the Prophet, sallallaahu ‘alayhi wa sallam, mentioned that Allaah The Almighty created cures for all the ailments he created.  [Al-Bukhari and Muslim]

It was also narrated on the authority of Ibn Mas‘ood that the Prophet, sallallaahu ‘alayhi wa sallam, stated that Allaah The Exalted did not create an ailment  without creating a remedy for it and the remedy could be known to some and unknown to others. [Ahmad].

However, you must stay away from sorcerers and charlatans because they never do any good. It was narrated on the authority of one of the wives of the Prophet, sallallaahu ‘alayhi wa sallam, that he forbade Muslims from going to soothsayers and threatened that whoever did so, Allaah The Almighty would not accept Salah (prayer) from him for forty days. [Muslim]

With regards to the objection of this girl's family to sending her to persons for treatment, if you mean sorcerers and soothsayers then this is her family's right and duty and you should encourage them in this because, as we mentioned, sorcerers and soothsayers never do any good. Rather they will cause her to become sicker.

However, if you mean treating her using Sharee‘ah-approved Ruqyah, then they should not refuse. If the young woman is your wife you may decide, but if you are still her fiancé, as it appears, then you can only advise them.

Allaah Knows best.