A novela oficial do filme afirma explicitamente que Isabel foi realmente a primeira escolha de Mammon:
And she understood then. Mammon had found another oracle. "Twins," she said breathlessly. She and Isabel had the same powers. In her, they'd been dormant, till lately. But the power was there. Mammon had lost Isabel - she'd sacrificed herself so that they couldn't use her to open the way for Mammon. But they had someone else. Someone quite handy.
Mammon could use Angela to complete the opening of the doorway; to populate Earth with the denizens of Hell; to make the unsuspecting world of men a literal Hell on Earth. Probably, Constantine mused, the flying demons hadn't been trying to kill Angela. Him? Yeah. But they'd have just captured Angela.
Notavelmente, a própria Isabel se considera escolhida (marcada) pelas forças do mal
She [Isabel] rubs her wrist-the mark there, the strange circular symbol that burns there... and she knows in her heart what it means. It means she's been chosen. And she can't let that happen..