[@Goliah]
Or
He can sense her.
She can be immune sure but he can tell that she's demonic.

Though technically wasn't lucifer possessing Richard (I think I remember that being the guys name) so biologically they would not be related

Lucifer did not possess anyone for Cole so biologically he is half angel half mutant 

Whereas biologically would she not be half human half demon?

Just thinking out loud so to speak