It might be a secondary character who has had a significant arc in the story. Without more context about the novel, it's hard to say exactly who she is. But she is likely someone who has had a particular emotional journey within the plot.
The significance could be that it represents a character's growth or a change in their emotional state. Maybe she has overcome some great sorrow or trauma within the story of the novel.
The devil in manhwa can take many forms. It could be a traditional evil character with horns and a pitchfork, or it could be a more symbolic representation of evil or temptation. It all comes down to the imagination of the author and the message they want to convey through the story.
To survive, you should build alliances with the right characters. Also, stay away from obvious traps and don't trust everyone easily. Keep a low profile when necessary.
Could be that there's some sort of connection or misunderstanding. Maybe she needed a place to stay or was looking for someone and ended up there by accident.