BS”D:
a) A woman may not be counted for a minyan
b) A woman may not lead a minyan
A minyan is needed for a Davar Shebikidusha, and requires 10 adult males. This is learned from the language of “Aidah” by the spies, of which there 10 spies that sinned, and they are called an Aidah.
From the Gemorah:
??”? ??? ?’ ???? ?? ??? ?”? ????? ???? ??? (????? ??) ??????? ???? ??? ????? ?? ??? ??????? ?? ??? ???? ????? ??? ???? ???? ?’ ???? ???? ??? ??? ???? ??? ??????? ???? ??? ????? ????? ??? (????? ??) ????? ???? ???? ????? ??? ??? ????? ??? (????? ??) ?? ??? ???? ???? ???? ?? ???? ???? ?? ??? ????
There is a discussion why women do not count. Some approaches are: may not be part of an Aidah (as the spies were male(seeming the GRA in Hilchos Birchas HaMazon)), or they are not Mechuyav in Tefilas Shmonei Esrei (or other Devarim Shebikidusha), so they can’t count for the minyan needed.
One who does not count for the minyan can not lead it, as the purpose of leading is to be Yotze others in the minyan, of which the leader must be part.
“Tradition” is not the answer that the Rishonim & Achronim give.