The Gemara in Niddah 50a says ?? ???? ???? ??? ?????. Tosafos asks that a woman is pasul as a witness yet she can be a dayan as we see from Devorah and from the drasha of ??? ???? ?????? ???? ????? ??? ???? ??? ?????? ?????? ??? ???? ???? ??? ????? ??????? ????? ??? ???????. Tosafos gives three answers. The first answer is that the rule of ?? ???? ???? ??? ????? only applies within the category of men. This would indicate that there is no problem with a woman being a dayan. The Pri Megadim in the pesicha in the beginning of Orach Chaim ??? ????? ??? ? writes that when Tosafos gives multiple answers the first one is the ikkar.
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