Is it Islamically permissible to take gold jewelry from one's mother-in-law without her knowledge, under the pretext of rectifying her financial injustice inflicted upon the husband and children? And how can the stolen items be returned if one does not possess the means?

A Muslim should not squander the reward for their good deeds or replace their virtues with sins. Your husband has done well by caring for and spending on his mother, and this is a form of charity that Allah accepts and multiplies. A son is not obligated to spend on his mother if she is self-sufficient, but if he does so, he is performing a voluntary act for which he will be rewarded. It is not permissible for the questioner to take any money or gold from her husband's mother, for everything she took is an unlawful transgression against the rights of others. She is obligated to repent sincerely, feel remorse, seek Allah's forgiveness, and return the value of the gold jewelry at its price on the day she took it, as it is a debt solely upon her. She can return it in installments secretly or seek the owner's forgiveness. If she has realized her past mistake and repented from it, she must rectify what is to come through sincere repentance and by restoring rights to their owners.