The damsel of the Sanct Grael (Holy Grail) is a minor character in Malory's Morte d'Arthur. However Rossetti included her in some designs illustrating the Grail quest, showing her offering the chalice to the knights, instead of Christ, as described by Malory. Rossetti's intention was probably to juxtapose her spiritual purity with the sinfulness of Queen Guinevere. Rossetti, like Tennyson, tended to emphasise the female characters of the Arthurian legend.
Here the damsel holds her right hand in a gesture of blessing. Her left hand clasps the Grail and a basket containing the Host. The dove symbolises the Holy Spirit.