Like, Kat is less intrested in 'dark' or 'light', and more in keeping the balance between the two. 

If a giant host of angels or entities of Light showed up, Kat would pick up her staff and try and kick them out as well. She want's earth for earthlings. 

She can't detect Lilith, because she's been subsumed inside of Susana. If Lilith flexed her demonic powers, Kat would notice.