[KappaKittyCat]

I'm sorry you've found yourself in this situation.

Your first stop should probably be the chapter's Treasurer and VP Standards or equivalent. If you haven't done this already, they can help you look into scholarship programs to cover dues. I know that my org has national and chapter-level scholarships to cover dues for women who can't afford to pay them. If you've exhausted all those options, then the best bet is just to be upfront with your big. Assure her that you adore her and that you are devastated about this (you sound that way, anyway), but that you have no other choice. If she's worth anything, she's not going to stop being your friend just because you can't afford to stay in your sorority.

Good luck.