Spoiler!
I'm assuming Nana is Kaya's aunt (the woman on the left side of the photo). It appears that Nana has taken possession of Kaya and is the reason why she can see ghosts and fight them. and probably relates to what is happening with her mother in some way.
๐ ๐๐ ๐๐๐๐ฃ๐'๐ค ๐ธ โ๐๐๐ผ, ๐๐๐๐ฃ๐'๐ค ๐ธ ๐พ๐๐ธ๐ ๐