Purdue Girlie,
Let me tell you a little of my family history.
On the night my Bis Sis, Sara, got
her Big Sis, Kim; Kim got into a severe car crash. The injuries were so bad that Kim could not come back to school for over a year. Sara was immediately adopted by Therese. When I joined, Kim was not yet back, so as far as I knew my family went Me, Sara, Therese. I then come to find out I have not one Grand Big, but two! I was way excited.
I tell this story because when I started asking questions I found out that there had been quite a few adoptions. So many in fact that when we took a picture of the whole entire family on bid day, the only ones not in it were the new pledges and about 6 other sisters!
My point is that even if you don't have an official Big Sis, all the sisters are your family now.
But to answer your question, I'd probably do some announcement at meeting and go shopping with your new Big for a set of family letters.
SK Love,
Carolyn