I wrote a letter as I think that.
A few days ago Rawls also discussed a matter with me, Sylphy's sticking way too much to Rudeus.
From Sylphy's viewpoint, Rudeus must be prince charming who rescued her from a hell-like childhood. Teaching her various things like an older brother, and finally realizing their difference in gender. Rawls also said, if Rudeus can win her over it will be for the best.