Thanks. Traded out death ward for it. Hmm. How about a twist on that? If you'd allow it, I'd like her to slowly gain the half-celestial template via the same mechanics you described, maybe spread out over 3 or four levels, depending on if you want to use the FR option gained template rule. The final part of it would have her gaining wings and exalted status. It'd make a kind of sense, especially if the demon is in fact helping to awaken her celestial heritage as part of that redemption package.
Barring that, perhaps having her do something suitably heroic/self-sacrificing and having her get the template that way. Either option would be fun to play. If we go the second route, I'd be happy to trade some of her ranger levels for clerical ones.