Is warning a woman about those who backbite her, with the intention of advising her not to reveal her secrets or trust those who are not trustworthy, considered backbiting that incurs sin?

Backbiting (namimah) is forbidden and is a major sin. It is not permissible except if it becomes the only means to achieve a desired benefit, and according to specific regulations. The woman concerned can be warned by advising her to keep her secret confidential, to be careful not to disclose it, and by reminding her of the Prophet's (peace be upon him) saying: "Seek help in achieving your needs through secrecy, for every possessor of a blessing is envied." This should be done without naming or describing anyone specifically.