Is it permissible for someone who vowed to donate a portion of her dowry to three charities, but was unable to fulfill the entire vow, to fulfill the vow from her work earnings? And is it permissible to change one of the specified charities in the vow to a more needy one?

A Muslim must fulfill his vow exactly as he vowed it. Therefore, he is obliged to give the specified portion of the dowry in charity to the designated recipients. It is not permissible to retract or substitute it. It is permissible to pay the vow from one's salary or other sources if it is impossible to pay it from the dowry. As for delaying fulfillment, there is no harm in it if immediate fulfillment was not intended or a specific time was not set for it, because fulfilling an absolute vow is not immediately obligatory, but it is recommended to hasten its fulfillment.