Only recently joined the Cantina, Dray was caught up in the middle of the Empress’s rise. She was separated from the Cantina but was determined to do anything she could to help. Making her way to the newly formed New Gallifrey and the Empress’s Citadel, she soon found herself in trouble and was saved by Lord Gregorius.
Susie's sacrifice refers to the event which essentially ended all conflict with the Chosen. Although the end of that arc was left quite vague, it was revealed in the opening arc of The GateWorld Cantina Chronicles what had really happened as a consequence of Susanne's sudden interference in the battle between Mapp and the last of the Chosen, Serena.
The Crusade of the Chosen refers to the war declared by the ancient Time Lord cult, The Chosen, on the universe shortly after their resurrection in the Temple of Time. It was their belief that a prophecy made just before the destruction of Gallifrey should be pursued, whereby they could take over the universe and gain ultimately power.