how has Emily been blinded by desire, irrationality, or mental illness ?

I have read a lot of interpretations about Emily but I am inclined to think that, somewhere along her life, she turned mentally deranged. The townspeople discover that Miss Emily has been living with the body of her dead sweetheart for many years. In Part II, the story about how the house began to smell takes place "a short time after her sweetheart - the one we believed would marry her - had deserted her." In Part III, when she buys arsenic from the druggist, she will not confirm that the arsenic is for killing rats. There is no explanation provided right away, but later the reader can assume that it was used to poison Homer Barron, Miss Emily's sweetheart. Was it her sheltered life or the death of her father that made Emily live with a corpse for so long? I'm not really sure, but I think she had mental issues.