You've got some interesting, creative ideas here. The main issue I see is that you will have to come up with some pretty amazing cause for the girl and her father to make them sympathetic. Even then you run the risk of it coming across as the ends (whatever good cause you come up with) justify the means (murder).
That's not to say the idea isn't worth developing, it just might be more challenging to come up with ways to make the protagonist engaging and (as you said) make the entire matter fit within a Biblical framework. In fact, if you can cross some of these hurdles, I think it has the potential to be powerful with lots of moral conflict, as Syleh wrestles with the morality of murder, her upbringing, and so forth.
At least that's my two cents.
