The line you ask about from "The Yellow Wallpaper" demonstrates that the cure prescribed for the narrator by her husband (and the male-dominated medical establishment as a whole) is failing miserably. It demonstrates that denying a depressed woman all intellectual and mental stimulation to cure her is ludicrous.
In Gilman's day the male medical establishment believed women were mentally inferior to men and that too much thinking made women ill. Doctors also believed that female mental illness was rooted in the ovaries (thus the term hysteria, another form of the word, hysterectomy).
The quote reveals a woman suffering from what we today would call post-partum depression finding mental stimulation any way she can. Forced to give in to her husband's every order, her growing insanity is a testament to the destruction of whatever relationship they once had. As she "sees" the wall paper come alive, the "distance"
between her and her husband grows.
The line you ask about doesn't directly deal with her relationship with her husband, but it indirectly exemplifies their decaying relationship.