Empress Theodora is shown here with a group of her attendants as they enter the Matronem area of the church.
Women were not allowed to participate in the religious services in the main area of the church.
Early churches had a "matronem" or balcony area where women could observe the rituals. (picture follows)

Theodora is richly garbed in royal purple, with a jeweled collar, long mother-of-pearl earrings, and a diadem.
It has been suggested that special mosaicists may have been sent from the court at Constantinople
to create the portrait heads of both Theodora and Justinian, as they are more realistic and less stylized than those of their attendants.

Theodora was the daughter of a bear trainer, and was a showgirl who was not "born to the purple", but
"rose to the purple". She used her position as Empress to press for rights of women.
She died prior to the completion of the church's completion.

The curvature of the image is due to the way the wall of San Vitale curves to join with the semi-circular apse.
It is therefore impossible to get a straight image from the floor of the church.