If you say that women are obligated to read the Megilah, their obligation to fulfill this mitzvah is on the same level as men, and if that is so, then they would be permitted to read the Megilah for men as well. For example, both men and women are obligated to light Chanukah candles and a woman is permitted to light for a man. On the other hand, if a woman is only obligated to listen to the Megilah, then her obligation is on a lower level and therefore she can not fulfill the male's obligation. Some who say that women are obligated to read the Megilah, say that they are not permitted to read the Megilah for men because of kavod tzibur. Although women may technically be counted as part of a minyan for Megilah reading, in practice woman are not, because it can create a situation of immodesty.
Women are definitely yoztie other women.