May Sei sense magic on your character? How much do you want him able to tell? The only magic around Rosa is the magic of SCIENCE. So no.

May he use this information to be a jerk to your character? See above.

May Sei's singing voice have a soothing effect on your character? How much? Yeah, sure - but you'll have to work really hard at it to cool her off completely if she's angry. She's the type who holds onto her anger.