The most common theory is that Jane is the unnamed protagonist and the narrator. Gilman uses an unreliable narrator to show her rapid mental health decline. The character refers to herself in the third person, rejecting the social norms and her former self.
Detailed answer:
The Yellow Wallpaper tells about a woman who has a mental condition. Presumably, it is postpartum depression. Her husband imposes a rest cure on her and imprisons her in an upstairs room. The character’s mental state gets worse. She thinks that a woman is stuck behind the yellow wallpaper. When the husband comes to check up on her, he sees that the wallpaper is torn. His wife exclaims: “I’ve got out at last, in spite of you and Jane.”
The story mentions Jane for the first time. It is unclear who the name refers to. The popular opinion is that Jane is the unnamed narrator. The longer the character spends in her confinement, the further she dissociates from reality. Eventually, she associates herself with the imaginary woman trapped in the wallpaper. This attempt to free herself from her husband’s oppression hints at the feminist theme of the story.
It also shows the character’s separation from the self. Jane rejects the previous identity and the imposed social roles. The physical action of tearing the wallpaper is the act of mental liberation.
Jane is the name of the character’s old self, as she remains unnamed throughout the story. Her final exclamation signals to the readers that she is free from her self-imposed prison, husband, and society.