Women and the Megillah
Even though the reading of Megillas Esther on Purim is a mitzvah restricted to a defined period of time, and women are generally exempt from time-oriented commands, there is the same obligation for women to hear the reading of the Megillah as there is for men.
The reasons, explains Rabbi Yehoshua ben Levi, is because they too were involved in the miracle of rescue from the genocidal plot of Haman.
There are two different approaches towards understanding the meaning of this involvement. Rashbam (Pesachim 108b) explains that it was a woman - Esther - who was the catalyst of the miracle. Tosefos finds difficulty with this approach, because the words "they too" indicate that the women did not have a primary role. The explanation favored by Tosefos is that they too were threatened by the genocidal decree, and are therefore equal beneficiaries of the miracle.
Rashi, in our section of the Talmud, writes that since woman have an obligation equal to that of men a woman is eligible to read the Megillah, and the man hearing her reading fulfills his obligation. This opinion, however, is contested by the Baal Hilchos Gedolos, who rules that the obligation of a woman is to hear the Megillah but not to read it, while a man's duty is to read it. His hearing it read by another man is, however, considered as if he read it himself. It is for this reason that women do not read the Megillah for a man. (Shulchan Aruch Orach Chaim 689:2)