On the other hand, Emily designed her own death.  She decided to live as a recluse, to keep Homer Baron from leaving her, and to take matters into her own hands.  She may never have gotten used to her father's death, or the loss of the old ways, but after her father's death, Emily was once and for all in charge of her own life.  Perhaps this was enough to make her happy?

I am not sure if there is a yes or no answer to the question.  We know from the story that she lived as a recluse and was the subject of gossip from the townspeople.  So I would assume that as she experienced the loss of the old ways and manners that she was unhappy.  She seems never to have gotten over her father's death.  There is also evidence of her being unhappy in love.  The macabre finding of her intended husband, Homer Barron supports this.  What makes this even stronger is that there are grey hairs found on the bed with Homer on it, indicating that she had recently been on the bed.  None of this speaks for a happy woman.

The language used in the text to describe her death indicate sombreness.  "She died in one of the downstairs rooms, in a heavy walnut bed with a curtain, her gray head propped on a pillow yellow and moldy with age and lack of sunlight."  The adjectives, heavy, gray, yellow and moldy support this tone.