Is the wife sinful if she does not repay her husband's usurious loan, which he took to buy a house, and he refused to register her share in the house in exchange for her assistance, even though he possesses other assets that could be sold to repay his debt?

The sin of borrowing with usury falls upon the husband due to his lack of necessity or need. There is no blame upon you for refraining from helping him repay the usurious loan, because the marital home is a right of the wife when the husband is wealthy. You must advise your husband to repent of this great sin, for usury is one of the gravest sins and its perpetrator is cursed.