When they stat her out, I hope she is impressive (perhaps even over the top). I'd prefer to see her as a wizard, if only to give her maxed out Knowledge: the Planes. An intelligence 34 would work (18 start, +5 Tome, +5 level bumps, +6 headband of intellect). A decent constitution is also desirable, around 22 (16 start, +6 amulet of health). An okay charisma would be nice but not necessary, just for the guys who always ask "what's her charisma?" Epic spells would be awesome, particularly some demon themed ones. In the Epic handbook, I think that Mordenkainen was the only spellcaster who actually had epic spells. As for prestige classes, I think Loremaster and Archmage might fit her well, although if she were a real twink she'd go for Fatespinner and Divine Oracle. However, no demonologist, that class is terrible. If I could pick her items, they'd include a cloak of resistance +5, rod of absorption, cube of force, and some metamagic rods.