That Stupid Ending

I knew it was coming from the moment he said he wanted Dr. Day to kill him, and it seems like she barely put up a fight, even after seeing the tape of Frost torturing his victims, and starting to fall in love with the devout Detweiler, before she allows him to possess her. Yes, I know that she was saving her coworker and Christopher, but she never seems to entertain the idea that if Satan exists, then surely God does too. I think it would have been better if she had actually grown in faith in BOTH entities and at least tried to use that to loosen Frost's hold. It just seems so abrupt.

"Fizz!"
"Buzz!"
"'AVE A BANANA!"