A teenage girl accused of murdering her mom and attempting to kill her stepdad covered her mouth and giggled in front of the court as proceedings got underway.

Carly Gregg was just 14 when she allegedly shot her mother inside their family home in Mississippi in March.

She is alleged to have then baited her step-father into coming home before shooting him twice and fleeing.

Police say she later called a friend over and asked them 'if she had ever seen a dead body before' before leading them to her mother's collapsed body.

Gregg was offered a plea deal of 40 years in prison, but turned it down and her legal team is instead pursuing an insanity defense.

On Thursday, as day four of the trial got underway, Gregg was caught on the livestream trying to fight off a bout of the giggles.

Gregg was watching a member of her defense team scrawl something on a piece of paper at the time. It is unclear what the note said. 

She then smiled and covered her mouth with her hand.

There was no audio available on the livestream to pick up what she said immediately following the incident. 

Gregg is accused of shooting her mom and attempting to lure her stepdad back to the home with a text sent from her mother's phone on March 19.

Rebecca Kirk, a licensed professional counsellor who saw Gregg on nine occasions in the weeks leading to the alleged crime, testified on Thursday about the teenager's demeanor during their sessions.

On February 14 - just weeks before the shooting - Gregg said that she had plans to read Crime and Punishment.

The 1886 Fyodor Dostoevsky novel follows a Russian nihilist who, in Kirk's words, 'is very intelligent... and has this obsessive thinking of planning to murder a woman.'

The character comes to the conclusion that extraordinary people are entitled to kill others for the good of society, and kills a pawnbroker with an axe.

He is eventually sentenced to eight years in a Russian labor camp, declared insane.

'When he was in the camp he was unrepentant and that he did not think what he did was wrong and thought that the woman deserved it,' Kirk told the court. 

The defense told the court Gregg never got around to reading the book. 

Kirk expressed that Gregg was a highly gifted student and patient who 'had been affirmed a lot in her life for being intelligent.'

'She was proud of that, but she also had a genuine love for learning,' she told the court.

'She was gifted, that's a clear fact. Sometimes when you're so gifted and different from others, you might feel lonely and a little bit more isolated.'

Raskolnikov, the murderer central to Crime and Punishment, finds himself a poor student convinced of his own brilliance before developing a nihilistic moral theory that, in his view, entitles him to kill his victim.

The court heard on Wednesday from psychiatrist Dr Andrew Clark, who said he believes Gregg 'blacked out' for up to 90 minutes on the day of the alleged offence.

But he also accepted that someone in Gregg's position would have a motive to 'fake' a mental illness.

Dr Clark told the court Gregg reported to him that she'd had 'auditory hallucinations' for years prior to the alleged crime, but the voices in her head had never 'commanded' her to do anything.

Gregg had confided in Dr Clark that she had started smoking marijuana, several times per week and was concerned that her mother would find out, the court heard.

The court heard she had used marijuana up until at least the day prior to the alleged incident. 

She had also been prescribed Lexapro and Zoloft - both medications for mood disorders.

She is charged with murder, attempted murder and evidence tampering, and faces a life sentence if found guilty. 

The court previously saw footage of Gregg wandering around her kitchen and texting a friend in March, just moments after shots were fired. 

Gregg is seen in the kitchen wearing a Nirvana t-shirt, pacing up and down the corridor.

She briefly disappears off camera before returning, holding something behind her back, and peering into the kitchen.

Gregg then walked off camera again in the opposite direction moments before three gunshots rang out. 

After the first shot, a woman was heard screaming, and then the room fell silent.

Moments later, Gregg was again seen camera, casually taking a seat on a stool near the kitchen bench and texting on her phone as her two dogs watched on.

Gregg's mother, 40-year-old math teacher Ashley Smylie was fatally shot in the face. 

Her stepfather then received a text from Smylie's phone, reading: 'When will you be home honey?'

When Heath returned home, police say Gregg shot at him, hitting him once in the shoulder.

The court heard Heath wrestled the gun from Gregg before she could shoot him again, prompting her to flee the scene.

Police say she then texted one of her friends, asking them to come over to the house due to an 'emergency'. 

When the friend arrived, Gregg allegedly asked her 'if she had ever seen a dead body before' and led the witness to her mother's body. 

Gregg's stepfather, who survived the attack, testified in court that he had seen his wife covered in blood when he got home.

He said Gregg had once been a 'sweet little girl' but looked like 'she had seen a demon' on the day in question.

'When I opened the door to the kitchen, the gun went off in my face before the door was three or four inches wide open.

'The gun flashed in my face. It went off two more times, but my hand was on the gun after the first shot, and I twisted it from Carly,' he said. 

Gregg is charged with murder, attempted murder and evidence tampering. The trial continues.