“To any other survivors in this nightmare, you are never alone, we are all behind you,” she added.

Wearing a light blue prison jumpsuit, Leifer was mostly impassive as she watched proceedings via video link from a nearby maximum-security prison.

Gamble described her as a “serious sexual offender” who had shown a “callous indifference” to the suffering of her victims.

She will not be eligible for parole for 11 years.

The offenses spanned from 2004 to 2007, when Leifer was in charge of the Addass Israel School in Melbourne and the two sisters were teenagers.

The school is part of a reclusive Jewish sect on the outskirts of the southeastern Australian city.

“It was a life in which Jewish laws and customs were very important and strictly adhered to,” Gamble said.

He also said this stifling environment, and Leifer’s high standing in the Addass community, made it extremely difficult for the sisters to come forward.

According to an indictment, Leifer assaulted one of the sisters in 2006 after inviting her home to “sleep over for kallah lessons” — a kind of pre-wedding etiquette class that includes sexual education.

On other occasions, Leifer told the students she was preparing them to be wives, prosecutors told the court earlier this year.

“This will help you [on] your wedding night,” Leifer said after one sexual assault, according to Lewis.

“This is what is good for you,” she allegedly said during another incident.

Leifer fled Australia in 2008 after one of the sisters told her therapist about the sexual assaults.

She eventually settled in the ultra-orthodox Emmanuel settlement in the occupied West Bank.

Australian police filed charges against her in 2012 and requested her extradition from Israel two years later, sparking a lengthy legal battle.