Is it necessary for a wife to perform sex whenever her husband asks her to do so, or can she refuse it if there is no mood?
Sexuality is a right by marriage that spouses possess. Therefore, spouses do not have a right to refuse the request of the other, unless there is an exceptional situation (being seriously ill or suffering from an infectious disease) or a compelling reason (being in the menstruation period or fasting).
One of the spouses’ responsibilities is to satisfy the other spouse’s sexual need. Responsibilities come first than the mood.
Both of the spouses have the same responsibility on answering the other’s sexual need. However, male physiology makes necessary for men to be in mood for sexual intercourse. In other words, an intercourse is physically impossible if the man is not in the mood. That makes the female partner, somewhat responsible for getting her partner into mood in these situations. If the male is unable to get into mood, he cannot be forced to it, as it is against his nature.
Women on the other hand, are always physically ready for sexual intercourse. They cannot refuse their husbands apart from the reasons given above in the first paragraph. Having said that, men are not allowed to just rush in the intercourse as Allah commands:
“Your wives are (like) a cropland for you. So go to your croplands as you please and make yourselves ready for it.” (2:223)