Well sure, but they also most probably weren't writing for a non-Japanese audience in the first place. Why would they care about us and our gaijin sensibilities?
At the end of the day unless the author/publisher gives us her intended name in English we'll just be arguing in circles here. Heck, I wouldn't even be surprised if it turns out her English name is neither "Sitoen" nor "Shitoen"; maybe it's something like "Seton," idk lol.
... Unless there's a novel reader who can confirm if her name the origin/s of her name?