Aurora is Lydia's mother. She died before the beginning of the series. Lydia looks up to her, and she is the inspiration behind Lydia's determination to become a good fairy doctor.
Aurora was born in the Highlands , to the Makhil family (which has deep connections to fairy folk). However, she later learns that she is not her parents' true daughter, but a changeling. This is because of a deal that was made with a family of fairies.
According to lore, a Seer sleeps in the Highlands, who will one day awake to lead the battle against the "Prince of Disaster". In order to awake however, he requires life energy that is more potent in women, and more importantly, women carrying fairy blood. In order to ensure that such women are available for the Seer's awakening during times of crisis, the Makhil family has for generations traded their first-borns with a particular fairy family's first-borns, and essentially cross-mated them, thereby strengthening the life energy of the offspring.
Aurora was one such changeling, but she rejected her fate and instead fled her homeland with Professor Carlton.
She died supposedly due to an illness. However, unknown to even her husband, she had once ventured into the Highland's and opened the Seer's coffin (19 years before the beginning of the series), and as such her life shortened drastically.