Is zakat obligatory on the amount agreed upon as a compensatory condition and recorded in the contract as a deferred dower?

The woman's mahr (dowry) is her property, and she is obligated to pay zakat on it. As for the money agreed upon with the wife's guardian, on condition that it be paid to her in case of dispute or separation, it is not part of the mahr. Writing it in the document as a deferred mahr does not change the fact that it is not her property, and therefore, she is not obligated to pay zakat on it, because one of the conditions for zakat to be obligatory is that the wealth must be fully and stably owned by the person paying zakat.