Is faith considered deficient for one who does not believe in jinn possessing humans, and are the pains, fatigue, and inability to study that a girl is experiencing an indication of jinn possession or sorcery, and what is the cure?

The touch of the Jinn is affirmed by the consensus of the Ahl al-Sunnah wal-Jama'ah (Sunni Muslims), as indicated by Allah's statement: "Those who consume interest will not stand [on the Day of Resurrection] except as one stands who is being beaten by Satan into insanity" (Quran 2:275). Whoever denies this after knowing the scriptural texts is considered deficient in faith. Treatment with Ruqyah Shariah (Islamic incantations) and prophetic medicine is recommended.