One of her top ten books about loneliness, as shared at Publishers Weekly:
The Wall by by Marlen HaushoferRead about the other entries on the list.
One of the subsets of loneliness literature is the disaster that leaves a single survivor, a genre that dates right back to Robinson Crusoe, marooned on his island. It's frequently deployed in science fiction – I Am Legend springs to mind. But you might also consider Marlen Haushofer's The Wall, a 1963 Austrian novel that deals with the travails of an unnamed woman who must survive in the rural landscape where she has been vacationing, after an unexplained event creates a transparent wall that seals her off from the outside world, with only a cow, a cat, and a dog for company.