Osanna was born in the village of Relezi in Zeta to an Eastern Orthodox priestly family named Kosić and was baptized "Jovana" in that tradition. Her father was priest Pero Kosić and her uncle was Marko Kosić, a monk with the name of "Makarije" who later became Eastern Orthodox Bishop of Zeta. Her grandfather Aleksa Kosić and her great grandfather Đuro Kosić were also Orthodox priests. She was a shepherdess in her youth, and developed the habit of spending her solitary hours in prayer. A story says that one day while watching the flocks, she saw a child lying asleep on the grass. Attracted by its beauty, she went to pick up the baby, but it disappeared, leaving Osanna with a feeling of great loneliness.