On "Shabbat Zachor," the Shabbat before Purim, we conduct the special "Zachor" reading (Devarim 25:17-19), a Misva which the authorities consider a Torah obligation. Some scholars raised the question of why Hazal did not institute a Beracha to recite before performing this Misva. Why are we not required to first recite the Beracha, "Baruch Ata…Asher Kideshanu Be’misvotav Ve’sivanu Likro Parashat Zachor," or something to that effect?
The Rabbis explained by noting that the Almighty does not rejoice upon the downfall of the wicked. Although we are indeed to commanded to eliminate the nation of Amalek and to read the section of Zachor to remind us of Amalek’s cruelty, this is not a festive Misva. The Rashba (Rabbi Shlomo ben Aderet of Barcelona, 1235-1310), in his responsa (vol. 1, 18), writes that we never recite a Beracha over a Misva that involves destruction, and for this reason no Beracha was instituted over the reading of Parashat Zachor. This is the reason given by the Kaf Ha’haim (685:29).
Strictly speaking, women are not required to come to the synagogue to hear Parashat Zachor. Nevertheless, women have taken upon themselves the stringency to hear the Zachor reading, in deference to the view that they are included in the obligation. Since many women are unable to attend the regular synagogue services on Shabbat morning, the custom has developed in many communities to conduct a special reading for women in the afternoon of Shabbat Zachor. Hacham Ovadia Yosef, in his Hazon Ovadia (Purim, p. 10; listen to audio recording for precise citation), rules that this is a proper practice, as it gives women the opportunity to fulfill this Misva. Although it is forbidden to remove the Sefer Torah from the ark for no purpose, reading Parashat Zachor for women and thereby bringing them merit is an important cause that warrants removing the Torah from the ark.
Summary: Strictly speaking, women are not required to hear Parashat Zachor, but it is customary for them to do so, either by attending the regular services in the morning of Shabbat Zachor, or through a special reading in the afternoon of Shabbat Zachor.