Pious tradition holds that she was at a banquet with a high ranking official, and she began relating her experience at the REsurrection fo Christ. The host, not believing her, was holding a boiled egg, and he held it aloft saying “Jesus no more rose from the dead than this egg in my hand is red.”
And immediately it turned blood red.
My daughter chose Mary Magdelene as her Confirmation Saint, and the medal she received depicts Mary Magdelene holding up a red egg. The medal is sterling, and the egg is done in enamel.
This , from Orthodo Wiki:
Paschal eggs
According to tradition, during a dinner with the emperor Tiberius Caesar, Mary Magdalene was speaking about Christ’s Resurrection. Caesar scoffed at her, saying that a man could rise from the dead no more than the egg in her hand could turn red. Immediately, the egg turned red. Because of this, icons of Mary Magdalene sometimes depict her holding a red egg. Also, this is believed to be an explanation for dyeing eggs red at Pascha.