I know this is repeating some of what was previously said...oh, well.
If I knew of someone who was expelled from the sorority, I would not consider her a soror. If she tried to act as if she still was in the sorority, I'd consider her worse than a perp! Unlike a perp, someone who was expelled knew what she had. She also knew what she was doing when she let it slip away.
Like was said, someone would have to do something really bad to be expelled. Anyone who would risk her pearls and jeopardize the existence of the organization as a whole has no love in her heart for the sorority. She is more concerned with keeping up appearances than with learning about and developing a greater appreciation for something that is larger than herself.