I used random cause you don't know her. For all anyone knows the member could be wacko.
But the main reason I agree w/ the practice is that when you leave school; at least in my sorority, you automatically gain alumna status. Alumna have no say in collegiate chapter votes. Actives/collegiate members only have voting priveliges (sp?) at their own schools. So a girl can't go visit another chapter and vote during a meeting. Being an affiliate member gives you voting priveliges at the new school.
I've said in other posts each Greek system is different. Suzy could transfer schools, hang out w/ the chapter for a month and realize she'd be just as happy keeping alumna status.
The month is a "getting to know you" stage. However, as much as I am for the probationary period and chapter vote; I've NEVER heard of a sister not being accepted.