He said supervision on the night of the fire fell below expected standards, in particular because the woman charged with looking after Bennett, who was employed by charitable trust YouthLink, had taken her two young children with her to Bennett's Child, Youth and Family (CYF) house.
The woman knew this was against company policy, but did it anyway because her husband was working late and couldn't look after them.
"I think potentially ... having the two children present compromised her ability to provide good supervision and care of the young person," Mr Lambie said.
He also questioned YouthLink's policy not to provide a phone for the caregiver, whose only option was to text her supervisor from her own cellphone in the event of an emergency.
The inquest was told that landline phones had been removed from Bennett's house because she had previously assaulted a youth worker with one.
However, Mr Lambie said the overall care provided by CYF and YouthLink was appropriate.
The caregiver, who has interim name suppression, said she found Bennett and about five other young people drinking on the porch the evening before the fire.
They were clearly intoxicated and had a nearly-empty box of premixed drinks and a tall bottle of spirits.
Alcohol was not allowed at the property so the caregiver told Bennett that her friends had to leave and the alcohol would be taken away.
"Tonya responded with extreme verbal abuse and graphic swearwords," the woman said.
Bennett left without saying where she was going, but returned later that night with two males.
Later, she heard voices that sounded panicked.
She went outside and saw the house across the road, which she knew belonged to Bennett's ex-boyfriend, burning fiercely.
Bennett disappeared into the night while the caregiver spoke to police.
The caregiver was asked whether she knew that there had been a crisis plan in place should Bennett return home intoxicated, which stated she must contact police and tell the teenager to go to bed.
She replied that she had not seen the crisis plan before, and that it would have been ineffective in the circumstances anyway.
"I wouldn't be here if I tried to do that to her. She's very physical. I've seen her have tantrums and I don't think I would have been successful in that activity. She wasn't ready to go to sleep. She was ready to party, to be honest."
YouthLink clinical supervisor Diana Bush told the inquest that Ms Chapman had ben "very welcoming and very kindly disposed towards Tonya, and Tonya was grateful for Lynette's openness."
The inquest before Coroner Morag McDowell is set down for three days.
