Well this is a terrible way to handle it. Honestly it would have been better if she had just returned to the village since she could use that position to poison the village against Sain.
She's so obsessed with him that I'm convinced she's actually horrifically down bad but has been stabbed in the back so many times that she's waiting for the other shoe to drop and justify her trauma
I wonder if this could potentially end with the criminal activity of his father being exposed. It would be a realistic way to nerf the ability of the main villain to act and put him off-balance.
Probably not how the series is going to go but it would be nice if there was actual positive development between the father and adopted daughter as a proper potential relationship.
So his skill activates on a skill being used, but doesn't that mean an attack without a skill will still be effective? Why not just beat him with normal blows?