Why is her room on the top floor?

I mean, I know it's a plot device, but it makes no sense that this invalid woman has a room on the third floor of her home. Once you get to a point where you are basically bedridden, wouldn't you want a room on the ground floor? So she can more easily get to the kitchen for some food, or open the front door. I know it's to create this claustrophobic atmosphere and sense of helplessness, but it just seems like a ridiculous way to live.