[@Lonewolf685][@Turboshitter]

Seyrun's plan is getting to shape since now she's the victim of the story. She doesn't want to turn Caster against Wes, as well, since this would most likely result in her death as well. Simply to earn a bit of sympathy from Caster, after all, Seyrun still believes someone as naive as Wes will get himself killed in no time then, if she upholds her word to the end, she may have the chance of taking on Caster.

Just for once, backstabbing isn't the best option for a magus.

EDIT: Furthermore, Seyrun is testing Wes' morals. After all, she's literally offering herself to him, which would at the very least be the same thing as jumping a few generations of his bloodline and getting some recognition in the magi society. Let's see if he's so different of the monsters he claim to hate?