"She thought the kids were still alive," said attorney George Parnham of Yates, who police say drowned her five children in June of 2001.
She was only tried for three of those murders and found guilty in each case.
Psychiatrists testified that Yates suffered from schizophrenia and postpartum depression, but jurors determined she knew it was wrong to kill her children and found her guilty of murder.
Monday night, Andrea Yates was transferred from the prison near Rusk to a Galveston hospital, after refusing food and losing more than 20 pounds. Parnham said she voluntarily drank something Wednesday.
Her husband, Russell Yates, also said Wednesday that his wife thought their children, who ranged in age from 6 months to 7 years, were still alive.
"On top of the medication, and her chemistry, and her underlying illness, she obviously has a tremendous amount of guilt over her actions and taking the lives of our children," Russell Yates said.
"She has a hard time having hope. ... She lost everything she loved," he said. He described her as "overtly psychotic."
This is not the first time Yates' health has declined since her arrest. In September, doctors had to forcibly medicate her when she refused to take her medication, her husband said at the time.
Her lawyer says he noticed the change in Yates as the anniversary of the murders approached.
"The closer she got to the anniversary, the more thoughts she got, figuratively and literally," says Parnham. "She started losing weight, going psychotic, and it's just not a good time."
"There is apparently a determination within her that wants to put an end to this," Parnham said. "I'm not sure what type of psychiatric medications can offset the reality of what occurred and make her feel better about that."
According to Parnham, Yates is down to about 107 pounds. Her Texas driver's license lists her weight as 126 pounds. She is 5-foot-7.
Yates, 40, has been placed on suicide watch at least four times since her children's deaths.
Within hours of Russell Yates leaving for work in June 2001, Andrea Yates called police and an ambulance to her home. She answered the door in wet clothes and told an officer what she had done.
She led the officer to a bedroom where the four youngest children's bodies were laid out on a bed. Police found the oldest, Noah, 7, floating face down with arms outstretched in the tub.