Pixie once lived in the ruins of an old, moss-covered castle, part of the Ancra Ruins just to the south of North Town (located on the Ancra side of the Mandy Desert). From here she controls several dig sites where her troops keep human slaves to mine mystery discs.
Her throne room is filled with Lost Discs, either because she routinely kills her troops in fits of rage (as she did with Captain Clay) or because the castle was the ruin of a battle site from the ancient war.
The Ancra Castle is also one of the exploration locations in Monster Rancher Battle Card, and at the end you can achieve the Pixie card if you beat the Talos that has taken up residence there.
Gallery
The Ancra Dungeon seen in MRBC
The Ancra Castle above the ruins
The castle drawbridge
Pixie's tower