spring tea question

Personal connection would be the first criteria. Somebody in the chapter knows you.
Second would be what the chapter is looking for - top grades, political involvement, athleticism, pageant titles, officer material...chapters strive to be well-rounded, and that changes every year according to who graduates, drops out or otherwise leaves.
Third would be numbers. How many do they need? the more they need, the larger the number of invitations.
Fourth, a chapter wants to establish connections. They want to get your daughter thinking positively about them.

HOWEVER....most are not terribly analytical. Most will target around 25%, and then mass e-mail everybody else.

And IN THE END....plenty of girls pledge sororities to which they never received a spring tea invitation.
So...relax. Just make sure her name is on the list.