Should a woman make up the 'Ishā' prayer after purification from menstruation if menstruation began before she performed it?

You are not required to make up the Isha prayer as long as menstruation began while there was still enough time left for one unit (rak'ah); this is based on the Prophet's (peace and blessings be upon him) saying: "Whoever catches one rak'ah of the Fajr prayer before the sun rises has caught the Fajr prayer, and whoever catches one rak'ah of the Asr prayer before the sun sets has caught the Asr prayer."