Colten Boushie's sister is alleging that she was injured by an RCMP officer, detained without charge and mocked by a guard over her brother's death, on the day after her family spoke out publicly about their treatment by police.

Satin Denny says she was stopped by RCMP officers on Oct. 22 on the Red Pheasant First Nation. Ms. Denny, whose younger brother was slain Aug. 9 in a case that has fuelled racial tension in Saskatchewan, said she was arguing with her mother and had just walked out the front door when police detained her and held her in a cell for several hours. She said she was left badly bruised by the encounter.

When she was finally released at 3 a.m., she insisted that RCMP officers take photographs to document her injuries, Ms. Denny said. She tried to file a formal complaint on the spot, but was told she had to wait. RCMP investigators visited her at home last week and she spoke to them for about an hour, she said. She has since sought treatment for ongoing pain.

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The RCMP confirmed that they have received a complaint from the public and said they are looking into it, but declined to answer questions in any further detail. They are prevented by the Privacy Act from confirming whether a person was held in custody if that person was not charged, so refused to say why Ms. Denny was detained.

Ms. Denny is alleging that her injuries occurred when an officer threw her against the side of a police vehicle, causing what she described as large bruises on her arms and chest. A photo provided to The Globe and Mail shows dark purple bruising near the centre of her chest, as well as black and yellow bruising over her right arm. She also says she was elbowed in the back.

The incident will further intensify scrutiny of the RCMP, which is already under fire for its handling of the investigation into Mr. Boushie's death. The slaying prompted demonstrations and aggravated a racial divide in the province. In the aftermath, Saskatchewan Premier Brad Wall issued a plea to stop the racist comments circulating on social media in the province.

Ms. Denny broke down in tears as she described the events she alleges took place on Oct. 22.

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"I felt like I was getting thrown around like a rag doll," Ms. Denny said. "I just remember I kept yelling 'Stop, it hurts. I'm not resisting.'"

The alleged incident took place the day after her family spoke to The Globe of their anger over the way they were treated by the RCMP following Mr. Boushie's death.

On the night Mr. Boushie died, his family says, the RCMP officers who notified the family also searched their home. They rummaged in closets, opened the microwave and shone flashlights on young children in their beds, making the family feel as though they had done something wrong, they said. The RCMP has described the family's account as concerning, but declined to address it in detail because the matter is before the courts.

Mr. Boushie, a 22-year-old indigenous man, was killed on a Saskatchewan farm belonging to Gerald Stanley on Aug. 9. A police warrant application says he was shot in the back of the head, and Mr. Stanley is charged with second-degree murder.

Ms. Denny said she had been drinking at a friend's house on Oct. 22. She arrived home to find that her mother, Debbie Baptiste, was upset. The two argued about a car and the use of a phone. As Ms. Denny walked out of her mother's home, her mother grabbed Ms. Denny. RCMP officers who were nearby saw the altercation and intervened, Ms. Denny said.

An officer spoke to Ms. Denny and placed her in handcuffs. She was angry and confused and pleaded for the cuffs to be loosened, as her right hand was hurting and turning purple, she said. The officer asked if there was somewhere else he could take her that night, and Ms. Denny suggested a cousin's house on the reserve.

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"I was doing everything he asked me to. I know better than to resist a police officer," Ms. Denny said.

Ms. Denny said that looked like the end of it, but things went wrong just as she was about to be released. Two officers were with her: one she described as tall, bald and muscular, and one she said was smaller. When the bigger officer grabbed her wrist to unlock the handcuffs, she jerked her hands away. She said it was a reaction to the pain in her wrist, but she believes the officer interpreted it as an attempt to resist.

"He thought that me jerking I was trying to resist and he turned me around and just [said], 'She's going to jail. Get her back in the cruiser,'" Ms. Denny recounted. Then she said the officer threw her against the side of his police pickup truck, pinning her arms behind her to reapply the handcuffs. She hit chest first, her sternum thrust forward by having her arms held behind her.

The officer then ordered her to climb into the truck, but with her hands cuffed behind her she found it difficult to get up.

She crumpled to her knees. The officer yanked to her feet by her arms, extending them in a way that felt unnatural and painful.

"To me, I felt like because they knew I was Colten's sister, and I don't know if these are the RCMP that were there [the night he died], I felt like they were attacking us. … After they picked me up off the ground I was standing there and I started crying," she said.

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"He just kept yelling at me to get in the truck and I remember trying to get in and I couldn't get all the way in and I kept falling back and I'm in pain and I'm trying to get in and I'm cuffed from behind and they just stood there, like didn't even try to help me or nothing. They just watched me struggle to get in that truck."

Ms. Denny, who is the mother of a nine-year-old boy, recently moved back to Canada from Montana to be closer to her grieving relatives. She believes police detained her that night for being intoxicated in public, and no charges were ever laid.

She was taken from Red Pheasant to North Battleford, about 30 kilometres away, and placed in a police cell.

After a few hours, Ms. Denny called out for a guard, asking if she could know why she was being held. The guard, an older white woman, responded dismissively, in Ms. Denny's telling.

"Why don't you go have a rally," the guard said, which Ms. Denny took as a mocking reference to her family's attempts to demand justice.

Mr. Stanley is free on bail and The Globe has revealed serious issues with the evidence in his case, including the discovery that the vehicle in which Mr. Boushie was killed ended up in a salvage yard before independent forensic tests were done.

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Ms. Denny said she visited a doctor last week.

"He referred me to get X-rays because he wants to make sure my back isn't fractured," Ms. Denny said. "His reaction was he was just stunned by it. Why would they do that? Why would they throw you so hard? He asked if I was fighting back and I said no."

"She's bruised," her mother, Ms. Baptiste, said. "When she came over [Friday] morning she could barely walk, and she can't lift anything."