What is she talking about when she mentions a smell creeping in the house

The narrator mentions that, in addition to its sickly and grotesque appearance, she hates the wallpaper's smell. She says that she did not really notice it much when the weather was nice and she could keep the windows open, but after a week of wet weather, the smell hangs heavily in the room.  She says, "It creeps all over the house." She can find it in the dining room and parlor, the hallway and stairs,...

The narrator mentions that, in addition to its sickly and grotesque appearance, she hates the wallpaper's smell. She says that she did not really notice it much when the weather was nice and she could keep the windows open, but after a week of wet weather, the smell hangs heavily in the room.  She says, "It creeps all over the house." She can find it in the dining room and parlor, the hallway and stairs, and even on her own person. Notice, however, that when she is finished describing the wallpaper's terrible "yellow smell," she says,

There is a very funny mark on this wall, low down, near the mopboard.  A streak that runs around the room. It goes behind every piece of furniture, except the bed, a long, straight, even smooch, as if it had been rubbed over and over.  I wonder how it was done and who did it, and what they did it for. Round and round and round—round and round and round—it makes me dizzy!

If we put two and two together (something the narrator seems no longer capable of doing), we can surmise that she has caused the "smooch" around the room. How else would she know that it goes behind almost all the furniture? How else would she become dizzy unless she herself were going in circles around the room? We do not get dizzy just by looking at circles.

As if to confirm this, the narrator reports near the story's end that "[her] shoulder just fits in that long smooch around the wall."  So, the narrator has been crawling around the room—or "creeping," as she calls it—and she is rubbing against the wallpaper, making it so that she smells it in her hair and on her clothes. Even Jennie, the narrator's sister-in-law, says, "that the paper stained everything it touched, that she had found yellow smooches on all [the narrator's] clothes."  So, the smell appears to creep all over the house, wherever the narrator goes, because the smell of the paper is actually on the narrator.