Is a wife required to break her fast to engage in marital relations with her sick husband, and is there any sin in that?

A woman is not permitted to observe a voluntary fast except with the permission of her present husband, based on the Prophet's (peace and blessings be upon him) saying: "A woman should not fast while her husband is present except with his permission." It is forbidden for her to refuse his request for intimacy. If she fasts without his permission, her fast is valid, though it is considered forbidden by the majority of scholars, and prohibitively disliked (makruh (definition) tahrimi) by the Hanafis, except for the Shafi'is who restricted the prohibition to fasts that are frequently observed. The husband has the right to break her fast through intercourse only according to the Malikis. As for an obligatory fast, she is permitted to observe it without her husband's permission, and he does not have the right to invalidate this fast.