BTVS: TALES OF THE SLAYERS
Not much has been revealed about Lucy Hanover, but what is known is that she was actovated as the Slayer Vampire Slayer somewhere in the 19th century, around 1866. She continued her duties until her death, where she became a guardian of the spirit world, helping lost souls to their rewards.
Lucy briefly returned to our world, to help the Slayer Buffy Summers halt the rise of the demon Ky-Laag. As a spirit, Lucy was able to possess an unconscious body, in order to help Buffy during the fight with Ky-Laag. After the demon's defeat, Lucy returned to the spirit world, in order to continue her duties.