A Florida mother has been accused of leaving her newborn daughter in a hot car to die while high on crystal meth – and she only realized what she’d done when a woman walked in on her masturbating in bed.

Megan Dauphin, 30, allegedly left her newborn, McKinley Garner, in a vehicle in Panama City for almost four hours on September 2, a day that reached 90 degrees in the afternoon.

The mom was arrested Tuesday and charged with the aggravated manslaughter of her child, who was born July 14. Dauphin is being held without bond in Bay County Jail.

Dauphin is set to make her first appearance in Bay County Court Wednesday afternoon, where she is expected to act as her own lawyer, according to court records.

Dauphin had left McKinley alone in the hot car for almost four hours on September 2 before a witness said she caught Dauphin in bed masturbating with her shorts unbuttoned, court papers show.

Upon being caught, Dauphin quickly moved her hands out from underneath the covers. The witness then asked the mother about her baby.

Dauphin said ‘Oh my God,’ jumped out of bed, and ran to the car, where she found her newborn, according to the documents.

Sheriff’s deputies were called to her Panama City home on September 2, and responders pronounced McKinley dead after unsuccessfully performing CPR on the infant.

Police executed a search warrant and found in a bathroom pipes that tested positive for residue of marijuana and methamphetamine.

They also found a blue vibrator ‘on top of all the other items’ on her nightstand, as well as spoiled baby bottles and food.

According to police interviews and surveillance video, McKinley was left in the car from approximately 9:15 a.m. to 1 p.m., where she missed a feeding as temperatures climbed toward 90 degrees.

Dauphin’s boyfriend told police he had left for work that morning at 6:30 a.m. while she was feeding McKinley.

He met up with her at 9 a.m. in a parking lot to give her cigarettes. The last time they spoke was at 11 a.m., he said.

Dauphin told police a similar story. She said she’d taken her older child to school that morning.

Dauphin denied to cops that she used drugs, but was heard telling a friend she was going to jail because of the drug test, police said.

An anonymous friend told Metro.co.uk that she had partied with Dauphin the previous weekend and called the incident ‘shocking.’

‘The Megan I knew would have never done this,’ she said.

The friend said she was disturbed by the image of little McKinley left alone to die in the car.

‘All I keep picturing in my head is that beautiful baby girl wrapped up in the swaddle blanket I bought off your baby shower.’

On July 30, when McKinley was 16 days old, police from nearby Lynn Haven responded to a call that a woman was asleep at the wheel of her car, court papers show. There they found Dauphin, who had overdosed.