Chinese authorities have pepper sprayed and shackled a Canadian woman who is a Falun Gong practitioner kept behind bars since February – and whose lawyer has now abandoned her after falling victim to local pressure tactics.

Early last month, detention house guards pushed Sun Qian to the ground and pepper sprayed her, before carrying her to a metal chair where they continued to spray her with the noxious substance until the bottle was empty.

Then, they placed her in handcuffs attached to foot chains. She was chained while she ate and went to the bathroom and also when she tried to sleep – with guards coming to check every 30 minutes and insisting they must inspect her restraints every time.

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Read more: Criticized for torturing lawyers, China lashes out at Canada and other countries

It was "a kind of unbearable mental torture," Ms. Sun said in an account given to her lawyer, which she then signed as accurate. It's not clear how long it lasted, but Ms. Sun's family believes it was for many days.

Once the billionaire joint owner of a biochemistry company with her husband, Ms. Sun began practicing Falun Gong in 2014. She credited it with curing her of health problems, and became a passionate convert eager to discuss her newfound faith.

Then in February, a group of men slipped into her villa in Beijing and took her away. More than a month later, she was charged with violating a Chinese law against superstitious sects, a common legal tool used in China's long campaign against Falun Gong.

Ms. Sun's case is one of several recent examples that have called back to the fore China's human-rights record, at a time when Ottawa is pursuing an ambitious trade agenda with Beijing.

In detention, Ms. Sun was forced to spend two months in the same pair of socks and underwear. After being pepper sprayed, she was kept in the same clothes for 10 days.

"I have been tortured so much that I really need to practice [Falun Gong] to keep my mental and physical health in good condition," she said in the account, which The Globe and Mail has obtained.

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But that lawyer is no longer working for her, after telling her family that local Justice Bureau officials pressured him and his law firm. One official asked him to become an informant on the case. Eventually, partners in his law firm told him that if he represents Ms. Sun or any other Falun Gong case, they "will cancel his contract to continue working with the firm," said Sun Zan, Ms. Sun's sister, in an interview.

No other lawyer has been willing to take on the case.

The Chinese justice system, meanwhile, has continued to press forward, saying it will proceed to the next step on June 28, which will include providing access to the evidence gathered and allowing Ms. Sun's counsel an opportunity to begin mounting a defence.

"But we don't have a lawyer right now," Sun Zan said. It has left the family "very helpless," she said.

At least one of Ms. Sun's supporters faults the Canadian government for the treatment she has received. She was placed in shackles days after John McCallum, the former cabinet minister who is now ambassador to China, appeared before a parliamentary foreign affairs committee in Ottawa. Asked about Ms. Sun, he said Canada disagrees with how China treats human-rights advocates.

But he offered no public comment on her case. "That doesn't always help, for the person in detention, if we broadcast their situation in public, so I think for those cases, almost all the time, it is better to proceed in a low-profile way," Mr. McCallum said in early May.

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Such a policy is "really dangerous," said Anastasia Lin, a beauty queen and human-rights advocate who has angered China with her dedication to Falun Gong issues.

China could see Mr. McCallum's comments as an assurance, Ms. Lin said.

"China just feels like they can do whatever and it won't have reputational cost. Canada isn't going to back this citizen up," she said.

"They're going to torture people anyway. But if the Canadian government doesn't speak up, that is likely to escalate further. The only way to stop that from escalating is when we talk publicly. Closed-door diplomacy has not worked in the past few decades with China."

Mr. McCallum, in a statement, said "consular services are being provided to the Canadian citizen who has been detained in Beijing," but said further details could not be released for privacy reasons.

"Canada takes allegations of mistreatment or torture of Canadian citizens abroad extremely seriously," he said. "Global Affairs Canada has put in place a mechanism designed to identify situations in which mistreatment of a Canadian may have occurred and to take steps to protect the interests and well-being of Canadians."

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Ms. Lin, however, has launched a petition calling on Prime Minister Justin Trudeau "to do everything in his power to secure her safe release," and speak out against China's treatment of Falun Gong practitioners.

She is in Geneva this week, where she raised Ms. Sun's case before the United Nations Human Rights Council. She also discussed China's broader campaign against Falun Gong.

"Will the United Nations turn a blind eye to such crimes against humanity?" she asked.

A Chinese representative, in response, said Falun Gong is an evil cult rather than a religion, and an organization opposed to China that Beijing has banned in the interest of protecting its own citizens.