Will I be sinful if my wife trims her eyebrows despite my forbidding her from doing so, and what is incumbent upon me to do about it besides advising her?

Trimming the eyebrows is considered part of namṣ (plucking) which is forbidden in Islamic law. The husband must continue to dissuade his wife from doing so with wisdom and gentleness, and inform her about the Ahadith (Prophetic narrations) that forbid namṣ and clarify that its doer is cursed and expelled from the mercy of Allah, until the wife is convinced and abandons this forbidden act.