"A Rose for Emily" by William Faulkner is not told in a strict chronology (we learn that Miss Emily is dead in the first sentence, for example, but she is alive for most of the story). Though we learn of things in Miss Emily's life in a non-specific order, we can still identify the moment in her life when we know that Miss Emily "has difficulty accepting reality."
When her father was still alive, Miss Emily seemed to accept his decision regarding all the unsuitable suitors, but she reveals her mental instability after he dies.
The day after his death all the ladies prepared to call at the house and offer condolence and aid, as is our custom Miss Emily met them at the door, dressed as usual and with no trace of grief on her face. She told them that her father was not dead. She did that for three days, with the ministers calling on her, and the doctors, trying to persuade her to let them dispose of the body. Just as they were about to resort to law and force, she broke down, and they buried her father quickly.
This revelation does not happen until the second part of the story, but it is the first moment in her life that reveals to us that she has trouble accepting reality in her life.
The first moment in the story itself when we realize Miss Emily is not fully in touch with reality happens in the first section, when she believes the story Colonel Sartoris made up about her tax situation so he would not have to talk with this Southern lady about money, something both of them would have found uncomfortable. When the mayor sends her a notice that her taxes are due, he
received in reply a note on paper of an archaic shape, in a thin, flowing calligraphy in faded ink, to the effect that she no longer went out at all. The tax notice was also enclosed, without comment.
Clearly she believes the outrageous lie that she owes no taxes because her father once loaned the town some money.
In either case, in her life or the story, the example is clear enough to let the reader know that Miss Emily is not living in reality but in a rather grotesque and distorted world of her own making.