I need help!

Hi everyone!
My name is Hannah and I am trying to do something really special for my aunt for Christmas. She was never able to join a sorority when she was in college, so I wanted to create a new one for her and the women in our family. We are all part of different greek organizations, except for her. I did not want this sorority to be school-based, because most of the women in my family have graduated from college already! I know that I have to get the greek letters approved to make it official, but I have no idea how to do that. I want it to be really special but I don't want to just throw a few greek letters together and pick a couple of colors and a symbol and call it a sorority. I want it to be official. Please let me know if you can help me!!