Is it permissible for a wife to take money from her husband by claiming she needs it for a medical examination and to buy her basic necessities with this money, instead of directly asking for an allowance, due to his dereliction in spending on her?

It is incumbent upon the husband to spend on his wife and children in a reasonable manner. If he fails to spend despite his ability, he has committed a grave sin. If the wife is able to obtain her own maintenance and that of her children in a reasonable amount sufficient for them, even without the husband's knowledge and without lying, she is permitted to do so. If she finds no means except through stratagem to secure her right and the right of her children, it is permissible for her. Medical treatment costs for the children are obligatory upon the husband, whereas for the wife, most scholars do not consider her treatment obligatory upon him.