SALVE REGINA! HAIL HOLY QUEEN!

QUESTION?

My Priest prays the Hail holy Queen at the gravesite before the burial of the deceased. Why is that?

ANSWER!

 "The Salve Regina is traditionally sung at the end of a priest's funeral Mass by the decedent's fellow priests in attendance" https://en.wikipedia.org/wiki/Salve_Regina. 
This prayer is traditionally one of the Marian Compline also known as Night Prayer, or the Prayers at the End of the Day. The English word Compline is derived from the Latin completorium, as Compline is the completion of the working day https://en.wikipedia.org/wiki/Salve_Regina.

Since death marks the completion of your life, your work and your end, it is fitting to pray the Salva Regina at the close of a persons life.