What is the ruling on informing a veiled female relative about a recipe for facial whitening and radiance, and what if she has already been informed and shared it with others, and does the ruling differ if another girl asks for the same recipe?

It is permissible for a woman to adorn herself with pure and permissible substances that whiten the face, provided that no harm results from it, and that she does not display her adornment before non-mahram (definition) men. However, if she intends to display herself immodestly (tabarruj) with this recipe, then it is not permissible to assist her in that. They must be advised and warned about the dangers of tabarruj, because a Muslim woman does not leave her home displaying her adornment to non-mahram men for fear of temptation. This includes anything that arouses desire, such as beautiful clothing and visible jewelry.