Is it permissible for a woman to offer a sacrifice even if her husband offers one, and what is the virtue of the sacrifice?

It is permissible for a woman to offer a sacrifice on her own behalf, even if her husband will also sacrifice, for the udhiyah (sacrifice) is a confirmed Sunnah for whoever can afford it without hardship. If a man sacrifices on behalf of himself and his household, that suffices for all of them, but he is not obligated to do so. Malik said: "A man is not required to sacrifice on behalf of his wife unless he wishes to; because it is an act of closeness (to Allah), and he is not obligated to seek closeness on behalf of his wife."