Spiridoula’s name day is December 12, the feast of Spyridon of Trimythous.
Churches that follow the Old (Julian) Calendar keep the same feast on December 25 of the civil calendar. See everything commemorated on December 12.
The saint behind the name

Spyridon of Trimythous
December 12, Hierarch, Σπυρίδων Τριμυθούντος
St. Spyridon, Bishop of Trimythous in Cyprus, was a shepherd of great simplicity and holiness who lived in the fourth century. Married and later widowed, he was made bishop while continuing to tend his sheep. According to tradition, at the First Ecumenical Council he demonstrated the unity of the Holy Trinity by pressing a clay tile, from which fire rose, water flowed, and earth remained in his hand.
Name days: Spyridon, Spyros, Spiros, Spirou, Spiro, Spyridoula, Spiridoula
Also celebrating on December 12
These names share the feast, many of them other forms of the same name:
Spyridon, Spyros, Spiros, Spirou, Spiro, Spyridoula
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.