SAN FRANCISCO, California (AP) -- Lashaun Harris had been hospitalized and prescribed drugs to quiet the voices inside her head.Still, legal and mental health experts say it will be difficult to prove the 23-year-old mother was legally insane when she dropped her three young sons to their deaths in San Francisco Bay.California is one of about 20 states that uses the strictest legal standard for assessing a plea of not guilty by reason of insanity. Under the rule, criminal defendants must show not only evidence of mental illness, but that they were incapable of determining right from wrong."Somebody may be very clearly psychotic and have a history of behaviors that establish the person was ... delusional, but that doesn't get you to insanity the way the law looks at it," said Ron Honberg, legal director for the National Alliance for the Mentally Ill.Harris, scheduled to return to court Friday, will most likely face a hearing to determine if she is mentally competent to stand trial, and psychiatrists eventually will attempt to determine whether she was insane at the time.Harris' lawyer, Teresa Caffese, refused comment last week on whether her client would claim insanity. Harris has pleaded not guilty to three counts of capital murder.On Wednesday evening, authorities said Harris lifted the boys over the railing of a downtown pier, dropping them one by one into the chilly 53-degree water 10 feet below. Authorities said she told investigators that voices instructed her to do so.The body of Taronta Greeley, 2, was recovered late Wednesday night about two miles from Pier 7. The other two boys-- Treyshun Harris, 6 and Joshoa Greeley, 16 months -- remained missing Sunday and were presumed dead.Relatives say the former nurse's assistant, who gave birth to her first child at age 16, suffers from schizophrenia that surfaced within the past two years and recently worsened when she stopped taking her medication.Harris' history as a struggling young, single mother may have exacerbated her condition, said Shari Lusskin, director of reproductive psychiatry at New York University Medical Center."She is a walking risk factor," Lusskin said.Rare defenseLegal experts say insanity defenses are used only in about 2 percent of all felony cases, and acquittals remain relatively uncommon. Mothers have had mixed success arguing they were not responsible for their actions because of mental illness.Christina Riggs, a nurse who injected her two sons with potassium chloride, the chemical used in executions, was put to death in Arkansas five years ago after an unsuccessful insanity defense.Prosecutors sought the death penalty for Andrea Yates, the Texas mother who in 2001 methodically drowned her five children in a bathtub. Despite an insanity plea based on postpartum psychosis, she was sentenced to life in prison.In contrast, Deanna Laney, a Texas woman who beat her two young sons to death with rocks, was acquitted by reason of insanity earlier this year.Prosecutors have not yet decided whether to seek the death penalty for Harris.Experts say the frequency of such cases points to the need for more aggressive monitoring of mentally ill mothers. In New York, for example, mothers can be ordered by a court to undergo treatment or take drugs to control their illness.Even making it socially acceptable for mothers to talk about the difficulties of parenting could help prevent such tragic outcomes, said Santa Clara University law professor Michelle Oberman."Imagine the life of a 23-year-old with three children under the age of 7, something that by definition includes a lot of struggle even if you are mentally healthy, even if you finished school, even if you are employed," said Oberman, co-author of "Mothers Who Kill Their Children: Understanding the Acts of Moms From Susan Smith to the Prom Mom.""It's ludicrous to think that a mother who is schizophrenic can parent a child, let alone three children on her own. It's a recipe for disaster," Oberman said.Copyright 2005 The Associated Press. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.