What was the rope she hid from Jennie for?

The rope was hidden to capture the woman in the wallpaper. From the text, we can infer that once she decided that she was the woman trapped in the wallpaper, she did, in fact, bind herself. She talks about deperation..... and the desire to jump from the window except for the fact that the bars were too strong.

But I am securely fastened now by my well-hidden rope—you don't get ME out in the road there!