As a young sorceress studying under the faeries, Xandra developed her magical skills and a jaded view of the faeries' influence on Neopia. The disillusioned Xandra decided to recreate Neopia to match her own vision. Attempting to make a world for Neopets ruled by a Neopet (her, of course), Xandra used the magic she'd learnt from the faeries against them, turning them all to stone.
This curse had consequences that not even Xandra could've imagined: without the faeries' power holding Neopia together, dark creatures emerged and preyed upon the very Neopets that Xandra hoped to empower. In the end, Xandra was thwarted by Hanso and turned to stone with her own magic. Her stone figure is now in the care of Queen Fyora, who still hopes to rehabilitate her most promising pupil.
According to one the Twisted Histories Capsules, in an alternate timeline, she succeeded by killing Hanso and Brynn and managed to keep Faerieland afloat.
Neopets: The Faerie's Ruin
Xandra was first introduced in as an anti-hero. King Altador comes into Xandra's place and finds her and the Ogrin Master researching. King Altador asks Xandra for help to figure out what caused the faeries to be statues. While having a conversation, Xandra spots Hanso leaving the scene with an important item in his hands. Xandra wants to destroy Hanso for the thefts he committed, but spared him and let him explain his occurrence with Hubrid Nox.
After explaining the story, King Jazan, King Altador, Ogrin Master, Xandra, Brynn, and last but not least Hanso, search for Nox.