I adopted my second little sister.
Her original Big Sis graduated and moved away, so she was a little lonely. Since we were close, I offered to adopt her. I got her a new lavaliere made with the date of the "adoption" and my name engraved on the back, and she got us matching sweatshirts with "Big Sis" and "Lil Sis" on the backs.
We exchanged the gifts during a sisterhood event with the entire chapter. It was so much fun!