In my experience, hospital stays are not the time when most people feel like tackling Proust (though all power to those who do). When I spent a week in the hospital, I mostly craved fun, breezy fare.
Obviously, choose books based on what you know of your loved one's taste, but I recommend Maria Semple's Where'd You Go, Bernadette for a clever, engaging, relatively low-stakes mystery; Tana French's excellent In the Woods is an incredibly engaging crime novel; and Jenny Lawson's memoir Furiously Happy is an implausibly hilarious book about severe depression.
You can find more of BuzzFeed's recommendations for laugh-out-loud books here, short books here, and plot-twisty books here.
Get Where'd You Go, Bernadette for $8.79, In the Woods for $10.39, and Furiously Happy for $8.79 on Amazon.