Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

An Arizona woman who police say confessed to smothering her three young children last month pleaded not guilty to first-degree murder Tuesday.

Rachel Henry, 22, said little in her court appearance in Phoenix, aside from affirming her name and date of birth. A not guilty plea was entered on her behalf.

Henry is accused of smothering her three children, who were 3 years old, 1 year old and 7 months old, on Jan. 20.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

An initial pre-trial conference is scheduled for March 24. Henry is being held in lieu of $3 million bail, according to online jail records.

Phoenix police have said in court documents that police discovered the three children deceased when officers were called to the home. Henry allegedly told investigators that she smothered all three, but a motive is unclear, according to the documents.

A prosecutor has previously said that Henry had a history of drug addiction, specifically methamphetamine, and that her children had previously been removed from her home because of drug issues.

A family member told NBC affiliate KPNX of Phoenix that Henry was addicted to methamphetamine and was acting strange in the days before the children died.

A makeshift memorial grows in front of the home where Rachel Henry was arrested on suspicion of killing her three children after they were found dead inside the family home earlier in the week, shown here Thursday, Jan. 23, 2020, in Phoenix. Ross D. Franklin / AP

Henry had recently moved to Arizona from Oklahoma, and the three children were laid to rest in Oklahoma over the weekend, the station reported. Police said in court documents that Henry told someone else in the home she was putting the children down for naps and that after they were dead she placed them on a living room couch as though they were taking a nap.

Pearl Rebolledo Velazco, the children's great-aunt, said at a vigil last month that she was at the home when the children were killed and that she was completely unaware of what was happening in another room, The Associated Press reported at the time.

"We had no reason to think otherwise that she was putting them down for naps," Velazco said. Velazco also said that she attempted to perform CPR to the 7-month-old and told Henry to call 911, but Henry was staring at her phone and Velazco called 911.