She is now a succubus!I like the concept. Succubus seems like a good choice to me, especially with the high charisma and the potential to use a whip as core concepts.
They mention doing that in this Duskblade handbook (Whoops! Browser Settings Incompatible).The Duskblade's abilities don't require that you use a spell on the Duskblade's spell list, so dual classing with Wizard or Sorcerer will provide you with the larger variety of spells to use with the Duskblade's channeling abilities.