Day Care Provider Allegedly Killed 'Happy, Healthy' Baby Girl by Giving Her Antihistamine

A Vermont day care provider is accused of killing a 6-month-old girl by giving her sedatives so the infant would take a nap, PEOPLE confirms.

Stacey Vaillancourt, 53, is charged with suspicion of manslaughter and child cruelty in the January death of Harper Rose Briar, the Vermont State Police Department announced in a news release obtained by PEOPLE.

Vaillancourt’s arrest follows a medical examiner’s autopsy, which found that Harper Rose had high concentrations of diphenhydramine, a sedative, in her body and died of diphenhydramine intoxication. Her manner of death was ruled a homicide.

The baby had been in Vaillancourt’s care for only three days when she died on Jan. 24.

On the day of her death, Harper Rose was dropped off by her parents at Vaillancourt’s at-home day care. She was “happy and healthy, smiling big like she always had,” the infant’s family wrote on a GoFundMe page.

However, later that day, police responded to a 911 call from Vaillancourt’s home and found the infant not breathing.

“Marissa and Blake got the call no parent wants,” the family wrote on the GoFundMe page. “Harper was unresponsive and headed to the hospital via ambulance.”

But Harper Rose was pronounced dead at the hospital.

“They had a lot of doctors working on her but it wasn’t enough,” Harper Rose’s father, Blake Briar, wrote on Facebook. “I’m so lost for words.”

• Want to keep up with the latest crime coverage? Click here to get breaking crime news, ongoing trial coverage and details of intriguing unsolved cases in the True Crime Newsletter.

Authorities immediately began investigating the infant’s death.

Diphenhydramine is an active, sedating ingredient in over-the-counter antihistamines, the police news release states. It is not to be used on an infant unless ordered by a physician.

Investigators were able to determine that Harper Rose was given the sedative without an order from a physician.

“The state is alleging that the defendant sedated an otherwise beautiful, happy, healthy 6-month-old to the point where that baby could not lift her head and died,” Rutland County State’s Attorney Rosemary Kennedy said, according to the Associated Press. “From the state’s perspective that is about as serious a charge that we see in Vermont.”

On Monday, dozens of Harper Rose’s family and friends attended Vaillancourt’s hearing wearing pink shirts that said “Justice for Harper Rose,” the AP reports.

“None of this seems real, I can’t sleep without seeing her, I can’t open my eyes without seeing her, I can’t do anything,” Blake Briar wrote on Facebook in January. “She was the best thing that ever happened to us and I promise me and mommy are always going to love you. I love you Harper Rose Briar, Rest In Peace my beautiful daughter.”

Vaillancourt’s attorney, Robert McClallen, entered a not guilty plea for his client. He did not return PEOPLE’s calls for comment Tuesday.

If you suspect child abuse, call the Childhelp National Child Abuse Hotline at 1-800-4-A-Child or 1-800-422-4453, or go to www.childhelp.org. All calls are toll-free and confidential. The hotline is available 24/7 in more than 170 languages.