The way in which Charlotte Perkins Gilman suggests a feminist theme in the short story "The Yellow Wallpaper" is by presenting us with a main character who is suffering a condition that is uniquely inherent to women. Furthermore, the ill-treatment of her condition and the lack of knowledge about it suggests that a very low value is placed on the wellbeing of females during the early part of the century.
In this story our main character is suffering from an obvious bout of post-partum depression and, what could be more, a massive and psychotic depressive episode.
The way that it is treated is by isolating the woman into a room with no opportunity to vent her frustrations; the room has no books, she cannot draw at leisure nor for the sake of therapy, and she is kept away from her baby. Her husband treats the whole situation as trivial, and attributes her condition to the weak nature of women. Even worse than that, both the husband and her doctor talk about her as if she were nonexistent, planning her present situation as if she could not speak nor think.
It is more than understandable that, after feeling trapped both inside and outside, she begins to imagine a woman trapped within the yellow wallpaper, and she also imagines that she is responsible for releasing her. This is why, in her last attack, she not only rips the yellow wallpaper, but she also collapses on the floor to the shock of her husband who, seemingly, still does not get what is going on.