Is it obligatory for me to pay zakat on jewelry saved for future marriage, which has reached the nisab and upon which a hawl (a year) has passed for several years, knowing that paying it will be done secretly from my mother for fear of her anger?

Zakat is obligatory on jewelry intended for hoarding, and it must be paid immediately when it becomes due. It is not permissible to delay it except for a legitimate excuse. If the sister cannot pay Zakat discreetly from her mother, she should try to convince her of the virtues of Zakat and that it does not decrease wealth. If the mother does not agree, the daughter is not obliged to obey her in refraining from paying Zakat, because there is no obedience to a creature in disobedience to the Creator.