One thing to keep in mind id that Beta is part of the Greek system at Purdue...correct?
Last time I knew only three chapters nationwide were part of thei schools greek system.
As for rush....We send home letter to all freshman and Sophomores in the summer. Our Associate Dean forwards a simular formal letter once at school (but to all females in the College of Ag & Nat Res) We chalk the walk, put up the sandwich boards, talk in classes (100 & 200 levels that have Ag majors in them) with an overhead about Sigma Alpha and invite girls out to the info sessions, have a mixer with AGR, dorm storm to hang up fliers, but them in ALL of the ag buildings, wear Sigma Alpha shirts like no other.
I'm sure if your president or rush chair talks with your chapter contact on national borad they can help you figure out a solid plan for next semesters rush