Can a woman be motze a man in brachos? Specifically, if they ate together and both would need to recite al hamichya. Would it make a difference whether the man and woman are married or related?
A woman may be motzei man with a bracha rishona. The reason is because both men and women have the same obligation to say a bracha rishona.
Regarding Birkat Hamazon (bentching) it would depend on how much each of them ate. If the man ate a full meal, she should not be motzei him. The reason is as follows. It is controversial a among the authorities if her obligation to bentch is biblical, or if it is only rabbinical. (The reason it would only be rabbinical according to some authorities is because they don’t have land in E. Yisroel and according to others because they don’t have the mitzvos of bris and torah learning). Therefore if he ate a full meal, and now he has a biblical obligation to bentch, she should not be moztei him, because it is not clear if she her obligation is on the same level or not. If he only ate a kezayis, (and therefore his obligation is also only rabbinical) and she at a full meal, then she may be motzei him, because their level of obligation is the same. If both of then only ate a kezayis, and are not full then it is
Regarding being moztei a man with al hamichya, a woman can be motzei a man with al hamichya. The reason for this is because there are three questions here, and each one has one side that she has the same obligation as a man. According to the authorities that a woman’s obligation to bentch is biblical. Another doubt, if al hamichya is biblical or not even for men, as there are authorities that it is rabbinical in nature. Another factor to add is that there are those that say that the reason women don’t bentch is because they don’t have the obligation of bris and torah, but both of these are not mentioning in al hamichya. Therefore numerous poskim have ruled that a woman may be motzei a man with al hamichya.
Brachos 20b, Shulchan Aruch O:CH 186-1, M:B 2,3, Birkas Moshe 12, Poskim