What is the ruling on a woman's vow to pray two rak'ahs if Allah heals her son, and is there anything upon her if she forgets to perform them after his recovery?

A vow (nadhr) is disliked, but if someone vows an act of obedience to Allah, then it becomes obligatory upon them to fulfill it. In this case, the vow is specified and conditional upon something happening, and it has happened, so it is obligatory for her to fulfill it. If she forgot to pray the two rak'ahs, she must make them up (qada'), because a specified vow must be performed when one is able to, and if the time for the vow passes, it becomes obligatory to make it up.