Ok first off: this is awesome. In like, every way.Since she wasn't a gamer, I didn't bother with giving her spells, and just told her that her character could perform any miracle that one of the Saints had... So she walked around with no armor and no weapon except for her walking stick, gave all her gold away to the poor, layed on hands on every last stubbed toe and booboo in town, and fed every last small furry forest animal she crossed paths with, lol. She enjoyed herself immensely.
Second: a thread about Curse of Strahd? And you want rules lawyers? It's like Christmas for evilbob! (Oh wait - it was Christmas!) No wonder I was mysteriously summoned to check this forum...
To the OP: personally, I think your creative tactic is great, and I would certainly allow it. I wouldn't think there's anything wrong with it, and it would work as you intend. However, please know that as others have hinted, the odds of you actually killing Strahd this way are about zero. I wouldn't worry about cheesing the game: the game is set up stronger than you might think. Although, yes: if your party collects all the major artifacts and uses them against Strahd, that will give you a chance to beat him whereas otherwise you wouldn't likely have one.