What is the ruling concerning the Farewell Tawaf for my wife who experienced istihadah after completing it and before departing Mecca, considering she had taken medication to stop istihadah before Hajj?

Your wife's circumambulation (Tawaf) is valid, and she is not required to repeat it, because she is not certain that the blood appeared before or during the Tawaf. The original presumption is that it did not appear, so her Tawaf is ruled valid. This blood is considered menstrual blood if it occurred during the time of menstruation; otherwise, it is irregular bleeding (istihada).