Petroula’s name day is June 29, the feast of Peter and Paul the Apostles.
Churches that follow the Old (Julian) Calendar keep the same feast on July 12 of the civil calendar. See everything commemorated on June 29.
The saint behind the name

Peter and Paul the Apostles
June 29, Great Feast, Πέτρος και Παύλος
The feast of Sts. Peter and Paul honors together the two chief Apostles. St. Peter, the fisherman of Galilee who confessed Christ as the Son of the living God, was foremost among the Twelve and, after his denial and restoration, strengthened the brethren and preached to the end. St. Paul, once a persecutor of the Church, was converted by the risen Christ on the road to Damascus and became the Apostle to the Nations.
Name days: Petros, Peter, Pietro, Pete, Pyotr, Pavlos, Paul, Pablo, Pavel, Panos, Petroula, Petra, Pavlina, Paula, Paulina
Also celebrating on June 29
These names share the feast, many of them other forms of the same name:
Petros, Peter, Pietro, Pete, Pyotr, Pavlos, Paul, Pablo, Pavel, Panos, Petra, Pavlina, Paula, Paulina
What to say on a name day
The Greek wish is Χρόνια Πολλά (Chronia Polla), “many years.” A call or a short message on the day is what people remember. See name day wishes you can send and what a name day is.