What is the ruling on her eating from the money of her brother who works in a usurious bank, given that she lives with her mother and has no income?

If the husband's wealth is mixed between lawful and unlawful, it is permissible to benefit from it, though it is disliked. However, if all his wealth is unlawful, it is not permissible to partake of it except out of necessity and to the extent of need. The husband is obligated to spend on his wife and children in a reasonable manner. It is not permissible for the wife to leave her husband's house without his permission, except out of necessity; otherwise, she would be considered defiant (nashiz) and not entitled to maintenance. The advice is to return home and live with the husband in a reasonable manner, and to strive in advising him to fear Allah and to treat others kindly.