Zarra was exiled from Zalach’ann because her inept husband attempted to stage a coup that ended quite unsuccessfully. She was found in labor by an adventuring group from Highcrest, who felt it would be suitably ironic to take a Drow slave. After she had given birth, she was taken to the surface as a slave to Erevan (who had been wounded and forced to retire) and his wife Sariel. The Eladrin also took Zarra’s child to raise as their own and instead of using the name her mother had given her — Venyx — called her Vella.
Zarra continued to teach her child, thinking she could use her as a tool for escape. This happened in a bizarre way however, as Sariel — concerned at Zarra’s continued influence on Venyx — allowed Zarra her freedom on the grounds that Venyx stayed in Highcrest. Zarra cared not for the child, and fled. She returned a year later with a significant Drow force, and eradicated Highcrest from the map. How she regained a footing in Drow society is unknown, but she has a bounty on Venyx with the Horizon Syndicate. Most noteably it is a capture mission, not a rescue.