Who is Mrs. Barbara Franklin from Curtain and what is their importance?

Mrs. Barbara Franklin is Dr. Franklin's wife. She is described as in her thirties, with big, brown eyes and a long, gentle face. She is thin and extremely pale. Mrs. Franklin spends most of her time in her room, and throughout the novel, her mood seems to swing from happy, chipper and healthy to sickly. In the end, Mrs. Franklin accidentally poisons herself in an attempt to poison and kill her husband.