There is an unfortunate widespread phenomenon in my Muslim country, as some Muslims, who believe that they are under a spell or the effect of magic, go to churches and ask priests to break these spells.
One of my female relatives went to a priest seeking a solution for her undutiful son ignoring our strong objection. The priest recited some words over some water and asked that woman to drink from it along with those who were with her. He also instructed her to recite certain parts from the Bible and the Torah alleging that if the Jinn heard such parts, he will never come back.
I know that this is prohibited, but I want to know the proofs and evidence with which I can convince this woman to stop doing this.
May Allaah reward you.

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, sallallaahu 'alyhi wa sallam, is His slave and Messenger.

Scholars have held different opinions regarding the ruling on seeking Ruqyah from the People of the Book whether they are priests, monks or others. Some scholars considered that this is prohibited, and others considered it permissible and each party has evidence to support its claim.

Shaykh Ibn Baaz is one of the contemporary scholars who was of the opinion that it is permissible for a Muslim to ask a Jew or a Christian to make Ruqyah for him provided that he does not belong to a people who are in a state of war with Muslims, and that the Ruqyah must be approved by the Islamic Sharee‘ah. This is because if the one who is making Ruqyah recites from the Torah or the Bible, then this would be a prohibited Ruqyah, and he must only recite the Quran or other Sharee‘ah-approved supplications.

By reviewing the scholars’ opinions regarding this issue, it becomes clear that, in principle, it is permissible for Muslims to seek Ruqyah from the People of the Book as long as they use the Sharee‘ah-approved Ruqyah, namely, parts from the Quran and Sunnah, names and attributes of Allaah The Almighty, or clear understandable Arabic words that are in no way ambiguous.

Nonetheless, we advise Muslims to keep away from disbelievers, even those who are considered from the People of the Book, and to avoid resorting to them simply because we have our own Sharee‘ah-approved Ruqyahs and enough types of remedies that would suffice us from seeking their help.

Allaah Knows best.