After Haman finished parading Mordechai through the streets of Shushan, he returned to his home mourning and with his head covered. The Gemara (Megillah 16a) explains that when Haman was leading Mordechai through Shushan on the King’s royal horse, Haman’s daughter overheard what was going on. When she looked down, she could not discern who was who, so she naturally assumed that Mordechai was pulling the horse on which her esteemed father Haman was sitting as he was honored throughout the streets of Shushan.
In her tremendous hatred for Mordechai, she took some garbage from her house and poured it onto the head of the person leading the horse, who she assumed was Mordechai. When he looked up, she was horrified to see that it was her father Haman. She was so overcome by emotion that she jumped out of her house to her death. This well-known incident is difficult to understand. Everyone has done things to his parents that he later regretted, but it should not make him suicidal, especially if it was only an accident. Why did Haman’s daughter decide to kill herself when she realized what she had done?
Rav Yitzchok Sorotzkin beautifully explains that Amalek is descended from Eisav, who excelled in one mitzvah: honoring his father. Even though the commentators discuss the sins that the Jews committed that caused them to fall into the hands of Amalek, they add that Amalek also needs their own positive merit, and their primary good deed is the mitzvah of honoring their parents.
This explains why Moshe chose Yehoshua to lead the battle against Amalek at the end of Parshas Beshalach, as Yehoshua came from the tribe of Yosef, who did not hurt his father Yaakov through the sin of selling Yosef like the other brothers, so he was the best candidate to lead the battle against Amalek who excelled in the area of honoring their parents.
There was another tribe that had nothing to do with the sin of selling Yosef: Binyomin, from whom Mordechai and Esther were descended, making them perfectly suited to vanquish Haman. Esther had the extra merit of having never caused any pain to her parents because she was born as an orphan from both her father and mother, and she was therefore the perfect foil to Haman. In light of this insight into the strength and power of Amalek and his descendants, it is now quite understandable why Haman’s daughter was so distraught over the pain that she inadvertently caused her father to the point that she committed suicide.