A judge declared the Lindsay Clancy trial a mistrial after a deadlocked jury returned Friday for the seventh day of deliberations, a day after the jury’s foreperson told the judge a single juror won’t follow the court’s instructions about reasonable doubt.

The extraordinary disclosure made Thursday in the form of a note delivered to the judge offered the clearest glimpse yet of what may be keeping jurors from reaching a verdict on whether Clancy is criminally responsible for killing her three children. If jurors ultimately cannot agree on a verdict, the judge could declare a mistrial.

Clancy, a 36-year-old former labor and delivery nurse, doesn’t deny strangling her children in the basement of their home in 2023. Her attorney, Kevin Reddington, argues that postpartum psychosis led to her actions, while prosecutors say she knew what she was doing.

Postpartum psychosis is estimated to afflict 1 to 2 per 1,000 women after delivery. Experts at the Cleveland Clinic describe it as a mental health emergency affecting someone’s sense of reality. Though most people with postpartum psychosis don’t harm their children, mothers with severe cases may try to do so.