Is it permissible for a wife to secretly take a small amount of her husband's money in exchange for helping him with his work and correcting his exams, knowing that she does not take money from him and wishes to bring joy to her needy parents?

If the wife helps her husband in his work, she has the right to ask for wages for that, and she may stop helping until she receives her right. It is not permissible for her to take from his money without his knowledge, unless he forces her to work without compensation. In that case, she may take from his money without his knowledge an amount equivalent to the customary wage (اجرة المثل), which is known as the issue of al-Zafar (taking one's right by force or cunning).