It is NOT separation based on sex - tell her it's like the US Senate and each sorority is a state.
As soon as there are 2 sororities on campus, an NPC should be formed. The older sorority must take the initiative to form the panhellenic. This isn't negotiable, this is an NPC rule that all its member chapters must follow. If the university doesn't want to follow it it should not have allowed more than one NPC on the campus.
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