Yang Feng Glan, known as 'Queen of Ivory, pictured during trial in a Tanzanian court

(CNN) A Chinese woman, nicknamed the 'Queen of Ivory' and thought to be one of Africa's most notorious traffickers, has been sentenced to 15 years in prison, Tanzanian authorities told CNN.

On Tuesday, a Tanzanian court found Yang Feng Glan, 70, guilty of smuggling 860 elephant tusks that authorities say are worth $6.45 million.

Yang Feng Glan, was sentenced along with her Tanzanian co-accused Salivius Francis Matembo and Manase Julius Philemon.

They were also sentenced to an additional two years in prison under Tanzania's Wildlife Protection Act, which they can convert into a fine amounting to twice the value of the ivory they are charged with smuggling. Authorities put this value at $12.9 million dollars.

The defendants have already lodged an appeal, the court said.

Tanzania's Director of Public Prosecutions accused Yang of running a sophisticated supply chain between East Africa and China, using her ties to the Chinese and Tanzanian elite to move ivory across the world.

After more than three years of uncertainty and delays in the case, conservation organizations say the sentence sends a strong message to traffickers.

"The government is taking wildlife trafficking very seriously," said Krissie Clark the executive director of PAMS Foundation,a nonprofit group that fights crime against wildlife and supported the Tanzanian task-force that arrested Yang.

"Today's sentencing is testament that nobody in Tanzania is above the law."

The landmark ruling marks one of the harshest sentences ever handed down to such a high-profile and well-connected Chinese national living in East Africa.

Tanzanian investigators told CNN Glan came to Tanzania in 1975 as a translator for a Chinese company that was building a railroad linking the port of Dar es Salaam to Zambia. She was one of the first Chinese people to learn fluent Swahili.

According to an interview she gave to the China Daily newspaper in 2014, she quickly fell in love with the country. She even named her daughter Fei, (or Feizhou) the Mandarin character for Africa.

In 1998, she opened a restaurant in Dar Es Salaam that became popular with both the Chinese expat community and wealthy locals. Officials say she used the restaurant and another property as a front for the illegal trade in ivories.

Before her arrest, she also served as the secretary general of the Tanzania-China Africa Business Council.

Tanzania, which some have called the ground zero of elephant poaching in the last decade, has been heavily criticized by conservation groups for its inability to stop the mass killing of its elephants. The East African nation lost 60 percent of its elephant population from 2009 to 2014 , according to data released by the Tanzanian government.

But local conservation groups say the election of Tanzanian president John Magufuli in 2015 boosted the fight against poaching.

"An attack on Tanzania's wildlife is seen as an attack on Tanzania," said Clark. "None of this would have been possible were it not for the political will of the President, John Magufuli, and his drive to stop wildlife crime and corruption."

In the past, it has been rare to see poaching ringleaders arrested and convicted, but since the creation of an elite national multi-agency task force in the country, there has been a massive crackdown on poaching.

In the past four years, several poaching rings have been dismantled and numerous lengthy 20 to 30-year prison sentences have been handed down to wildlife traffickers, according to PAMS Foundation.

The decline in poaching in Tanzania has also been aided by recent strides by the Chinese government. In 2018, China, which has long been one of the world's biggest ivory markets, banned all trade in ivory and ivory products in the country.