This is no perfect build for her.
Sure you could go all out AP, Rylais, Rabadons, Abysals, Zonyhas, Sorc shoes...etc
Or you could go for a Spell Vamp mix, Ryalis, Gunblade, Rabadons, Sorc / Merc
Or if you get focused alot, you may be forced into building some tanky items to last a bit longer.
Core items, AP and SpellVamp-ish.