What are three points that prove the theme of women being powerless?In my mind, the theme of the story is how the woman, the narrator, is...

It is very evident the narrator of "The Yellow Wallpaper,"
the wife, feels completely powerless; when she does attempt to stand up for herself and
make suggestions that she feels would better her condition, those ideas are dismissed or
even laughed at.  This sad truth is evident in the narrator's conversations, thoughts,
and activities.  Those around her do not give credence to her perspective or consider
that she is more aware of her own condition than another person could be; when the
narrator addresses the topic of her own well-being, her husband, John, who is a
physician, acts as though there is no possibility that she could offer valuable
insight.

Near the beginning of the story, the narrator
describes her husband.  She states that he "laughs at {her}, of course, but one expects
that in marriage."  In addition, she feels that he is practical, impatient, far from
superstitious, and "he scoffs openly at any talk of things not to be felt and seen and
put down in figures."  The narrator goes on to exclaim that her own husband, despite her
assertations, fails to agree that she is ill.  Immediately after making this point, the
narrator asks, "And what can one do?"  The asking of this question makes it very clear
that the narrator feels there is, in fact, nothing she can
do.

Later in the story, the narrator tells the reader that
John laughs at her about the wallpaper.  It appears that John originally intended to do
away with wallpaper, as well as other unsettling aspects of the room, but then decided
it was not worth the money it would cost to do so.  Despite his wife's feelings about
the subject, he persists in his own opinion that "the place is doing {her} good."  When
she asks to change bedrooms to one that is downstairs, he calls her "a blessed little
goose" and fails to take the idea seriously.  John's lack of sensitivity to his wife's
suffering is reinforced when he jokes that "she shall be as sick as she
pleases."

One of the most obvious places in which a theme
of powerlessness is suggested is in the narrator's detailing of what takes place behind
the pattern of the wallpaper.  She believes that the woman behind the pattern, who is a
represention of herself, struggles to escape her confinement
there.

Then
in the very bright spots she keeps still, and in the very shady spots she just takes
hold of the bars and shakes them hard. 

And she is all the
time trying to climb through.  But nobody could climb through that pattern--it strangles
so; I think that's why it has so many heads.

They get
through, and then the pattern strangles them off and turns them upside-down, and makes
their eyes white!

Clearly,
the narrator wants to escape the sense of confinement and helplessness imposed up on
her.