She had failed. It should not have surprised her as much as it did. After over thirty years of one failure after another, it's actually surprising to succeed. She didn't know why she expected otherwise anymore. It was silly to think she could accomplish anything with her miserable existance. All she had ever brought was pain to those who she loved. All she ever brought was death or at the very least misery to those who tried to loved her.
She was called the Wicked Witch of the West, a vile, hateful nickname and she couldn't even live up to it.
As with everything else, she had failed. Madame Morrible was dead, but the Wicked Witch of the West had had no hand in it. The old fishy crone had popped off by her own accord. All the same, in some attempt to feel powerful, the Witch had bashed her head in. It made her feel slightly better to mutilate the corpse but the feeling faded. Her momentary triumph fizzled.
On some level, she was aware of her own steadily growing maddness. She could see that murder was not the task she should have given herself... but after a life lengthened by pain, she couldn't fight the desire to cause others harm... or at least, the Wicked Witch of the West insisted upon that.
But a voice, a voice that sounded like the old woman whispered in her ear that the so called Wicked Witch of the West wasn't so Wicked now, was she? No, she had not succeeded at being cruel. She could not bring pain to those she wished to. It was a sick joke. After bringing nothing but destruction, now the power to voluntarily end a life was denied to her.
Inside, a younger, less jaded woman was pleased to know that she had not actually killed. However the Witch was in control now. And the Witch couldn't see past her own failure at Wickedness. Elphaba looked at her past failures to be Good.
She had failed. It should not have surprised her as much as it did.