Shami-Amourae has 22HD which means she should have eight feats, not seven. As long as we are looking at feats for her, Combat Expertise is useless when relying on spell-like abilities, and against 18th level PCs Flyby Attack is no better. Combat Reflexes is also pretty questionable, although at least she can try and use it as PCs attack the chokesnake.
So some decent additions/substitutions to her feat list:
Quicken Spell-Like Ability(greater dispel magic)
Quicken Spell-Like Ability(unholy blight)
Maximize Spell-Like Ability(unholy blight)
Empower Spell-Like Ability(unholy blight)
Best tactic is too start off with blasphemy and just keep casting it while hitting the PCs each round with a Quicken SLA until she runs out of Quickens, and then try to use plane shift or energy drain.