OK, I know this thread is a few months old, but it strikes pretty close to home for me...
I was a member of a local sorority that went national.
As I understand it ~ if a local sorority approaches Panhel and says "we want to become a chapter of a national sorority" the local gets to choose the national. If Panhel decides a new national should colonize (before a local approaches), Panhel picks the national; but if the national Panhel chooses to colonize and a local sorority interested in becoming part of a national sorority are mutually interested, the local becomes the new colony. (Correct me if I'm wrong)
Anyway ~ to siglambshsu ~ congrats on Tri Sigma!