Is a wife sinful if she is unable to treat her husband well and be a good spouse to him due to his bad character, and what should she do in this situation?

It is the right of both spouses to be treated kindly, in obedience to Allah's saying: "And due to them [the wives] is similar to what is due from them [the husbands] upon a reasonable basis." A husband's ill-treatment of his wife and bad manners towards her contradict this divine directive and prophetic guidance. The wife should advise him kindly, strive to reform him, and seek help from Allah and from good people. If he persists in his behavior, she should fear Allah concerning him and fulfill his rights. Even if he does not fear Allah concerning her, she is not permitted to treat him badly, even if he treats her badly. Some scholars have gone so far as to permit her to withhold his right if he is the oppressor, but perhaps patience is better for her than retaliation.