Consider replacing some ur-priest levels with a PrC that advances divine casting. And take Practiced Spellcaster so that her spells are CL10 (which should match the other characters in the party).
EDIT: Ah, here's a way to make the casting Cha-based. Sorcerer 1, Precocious Apprentice, and the geomancer PrC.
EDIT2: The reason Races of War says to increase the CR for PCs is because PCs get to roll stats rather than the standard array, and they get +1 to an ability score every four levels. Those ability scores should be higher (subtract 10 from the basic succubus's score to find the racial bonus, subtract another 1 if the number is odd, then roll for abilities or use pointbuy as you prefer).