I also think there's some way in which Eunah herself is different from the other girl, because of all that suddenly starting seeing ghosts out of nowhere, and really close and personal, while the other girl claims she only saw them from a distance.
Σ(っ°Д °;)っ oh!
u get the point there... yeah, that can be too...
but, didn't Eunah saw him cause of an accident?! i mean she's awake all night on the day she saw Sin from a distance too.
The thing is, there seems to be a difference between the two girls because Hye Jin didn't say anything about ever having ghosts chasing her and wanting to eat her before her husband came and marked her, lthe way it happened with Eunah. Sin and snake boy explained to Eunah that before Sin marked her, ghosts used to go after her because she smelled delicious, and they said she smelled like that because humans who can see ghosts give off a particular smell that makes ghosts want to eat them. If Hye Jin could ever really see ghosts as much as Eunah could, she would remember having had ghosts stalking her and wanting to eat her due to her smell, before her ghost boy came and marked her. The fact that she was never chased by ghosts means she was never a tempting "meal" for them, and that is probably because her smell wasn't as "delicious" as Eunah because her ability to see ghosts was not as strong as Eunah's, and neither was she tempting after getting a ghost for a husband, because her husband's powers were not as strong as to tempt the strong ghosts to go confront her in order to eat her and steal those powers.
So, all in all, it seems Eunah's situation is different from Hye Jin's not only because she's married to a more powerful ghost, but because for some reason or other she was already tempting ghosts even before her marriage. Or at least, that's what I think... ┑(・ω・)┍
so, maybe... Hye Jin husband is in different level (lower) from Gi Sin and the serpent