Nice ideia

Thanks I thought it would be an interesting question! Ever since Faith helped Angel get his soul back I've wondered how awesome it would be if Faith found redemption as a Christian.

I think Joss Whedon tried to keep the show as non-religious as possible while sticking to traditional vampire mythology which contains some religious symbolism. That's why you have mentions of the PTB instead of any named deities. Having a major character become Christian could counteract that, especially if you tied it into her redemption arc, which works successfully without any religious attachment.