I say, and with God's success: It is necessary to fulfill the vow, and it is obligatory; it cannot be waived. It is permissible for her children to pay on her behalf, and they can either sacrifice a calf or donate the equivalent value of a calf as they see fit. She can also estimate the value of the calf, for example, 800 dinars, and then pay it off gradually as it becomes feasible for her, of course, all of this is contingent upon the condition of the vow being fulfilled, which is the healing of the son. And God knows best.