Thank you for a lot of suggestions.
Shapechange certainly seems to be useful. But as Runestar has pointed out, it may slow the game down. The player is playing 3.5e for 3 years but recently she seems to be somewhat overwhelmed by the complex rules of higher level spells.
Energy Drain seems to be promising, too.
Shades, while interesting, will not be a good option. The PCs will spend a lot of their time in outer/inner planes. So Illusion (Shadow) spells won't work.
By the way, I recalled one thing. The sorceress knows Arcane Spellsurge. So, she can cast 1-round spells such as Summon Monster IX, with only a standard action. That is something other casters can't.