What is the ruling on accepting in-kind and monetary gifts from a female relative of her husband who is among men of authority and wealth, given that she has no interest in it and is unable to repay its value?

The Islamic Sharia (definition) encourages gift-giving among people, especially relatives, and considers accepting a gift to be recommendable. The basic principle of a gift is that no compensation is expected for it, unless stipulated by the giver or established by custom, in which case it becomes a gift of recompense. Therefore, there is no impediment to accepting gifts from your relative, and you are not obliged to reciprocate unless she stipulates it or custom dictates, though reciprocation is better. However, if her husband's money is from unlawful sources, it is preferable to avoid accepting her gift.