He called her into his office and said, "Y'all graduated ...
FYI, no southerner would say this. "Y'all" is plural pronoun. A southerner would, when speaking to one person, say "you."
A Pittsburgh southsider would say, "youns" which is the plu-perfect contraction of "you ones" maybe used singular or plural, past, present or future tense, such as, "What did youns do with the gum bands?" or "When are youns gonna rid up this room?"
Uh, been to Arkansas much?
The plural is "all y'all."
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)