It couldn't be.
How could it possibly be? How was she able to defeat her? She didn't have the strength, she didn't have the power, she didn't have the faith The Father put into her. Yet here she was, resisting to the Bliss, resisting to the beautiful world that she wanted to give her. Faith didn't understand. She had shown her the path, offered here to guide her to the garden, where she would be safe for the miserable world she was part of. When all that didn't help, she had to use more… persuasive methods. She didn't want to. But she had to. She didn't want to betray The Father, or was it the wrath that he would unleash upon her if she didn't follow his orders? That thought was confusing. The Father loved her, he didn't want to hurt her. Yet that was the first of doubts that revealed themselves when the Deputy didn't give in once she killed the marshal and the mayor. She had expected her to give in after that, but she didn't. Instead, Faith saw something starting to burn in her eyes… something which scared her. At first she thought it was the fire of the Great Collapse; the sign that this lady was indeed the emissary of the Devil, coming to take her for an entirety in hell. She'd be a martyr. Then she realized it was nothing like that, and it was instead a feeling she knew herself; grief, anger, rage. Who she had been before she met the Father. Robbed of her friends, her life, her purity. All of that came back to her in a few, burning strikes. It had hurt. A lot. Everything had come to fall down around her, collapsing like the mountains in the prophecies of The Father. It was when Rachel emerged; the Rachel she had tried to suppress, the Rachel which made her weak.
And it was then that she fully realized the Deputy could really defeat her, maybe even kill her, and she began to scream: "It's not my fault! None of this is my fault! You think I wanted this? He plied me with drugs, he threatened me! I was seventeen! I was just a child!"
But the Deputy didn't listen. She really was going to kill her. Maybe she had it coming all along. In those last moments, where she felt her body being drained from faith and life, bullets penetrating her limbs, she accepted it. Broken, injured and lost, rejected by the Deputy (who backed away with a look of disgust on her face as soon as she reached out to her), she accepted that she was alone after all, and she just let go.
"You'll be the hero. And then... you'll choose."