Not sure what CVIII cites as her motivation for fighting but in Judgment I distinctly recall Sypha being spared from death by the church in exchange for her service to them, and her fellow witches are still being hunted down and oppressed. Sypha being a "good" witch genuinely seems to disagree with Dracula's methods, but her being forced by the church would be added incentive to combat him. Probably one of those gray areas in the series.
hmm, i think i know what you're talking about, but i didn't read it that way
"Granted protection of the church, Sypha vowed to hunt down the forces of evil and help mankind, despite their continued oppression of her sisters."
i don't know if the protection she got from the church was predicated on her making that vow, but i see what you mean, its possible. i guess i tend to tie that statement from the translated Dracula's Curse that says "Sypha lost his parents when he was young and was found wandering near the monastery, where he remained at the once-beautiful Wallachia. " i tend to think she was found when she was young after her parents were killed by humans (not necessarily the church), raised by Monks, granted protection by the church from other humans (not necessarily the church as a whole, but possibly rogue clergy, though it might be protection against general church policy), made a deal with spirits of her family to grant her power, and then made a vow to hunt down evil and help mankind.