What is the ruling on one who does not believe in the evil eye, and what is the ruling on saying to her, "Do you intend to disbelieve? This is the word of the Messenger of Allah, peace and blessings be upon him"?

Denial of envy is a repudiation of the Quran, and denial of the evil eye's effect is a reprehensible innovation (bid'ah). The evil eye is real, as proven by the Prophet, peace and blessings be upon him. One who denies its effect does not become an infidel, but rather falls into innovation and misguidance, and the correct view should be explained to him. Your objection to that woman is valid, but accusing her of disbelief for denying the evil eye is wrong. Instead, you should have explained the authenticity of the hadiths and clarified that her denial is an innovation and misguidance.