BILLINGS -- A Northern Cheyenne criminal investigator died Thursday while awaiting a double lung transplant.

Denise Phoenix, 43, was in line to receive a donation and was flown Thursday to Denver to await a transplant.

"Denise was a great human being and a great agent," said Matthew Pryor, special agent in charge of Bureau of Indian Affairs law enforcement in Montana.

Phoenix had vasculitis, which according to the National Institutes of Health is an inflammation of the blood vessels that occurs when the body's immune system attacks the blood vessels by mistake.

Phoenix had been fighting the vasculitis since last fall, Pryor said, after she came into contact with a substance on a table during a criminal investigation.

"The chemical seems to be the catalyst that led to these health issues," Pryor said.

Although her death wasn't with guns blazing, it was in the line of duty.

"She went out silently, investigating crime in Indian Country, going after these guys," Pryor said. "It's the reality of the dangers of what agents do."

Funeral services for Phoenix will be Thursday in Nevada. She was from Pyramid Lake, Nev.

BIA officers and agents from around the country are expected to attend and will provide an honor guard including escorting her body from a funeral home in Reno to Nixon, where services and burial will take place.

"She was impactful and the people she had worked with want to participate," Pryor said.

Survivors include Phoenix's husband, Thomas Smart, who is a sergeant with the Crow Police Department.

Pryor hired both Phoenix and Smart when he was working in Arizona and trained them both at the Indian Police Academy in New Mexico.

Phoenix worked her way up from being a tribal officer to one of the first female agents in the bureau.

She was a dominating force physically, administratively and with her big smile, Pryor said. Tall in stature, Phoenix could be intimidating when she wanted to be, he said.

She could tussle with the toughest of suspects then return to the office to fix her lip gloss and hair.

Fellow agents characterized Phoenix as a woman who loved her work. She had a passion for solving crimes, especially those against children, and was known for always striving to refine her investigatory skills.

"She always had questions, always wanted to learn," said John Oliviera, a former BIA special agent in charge who was her boss in Nevada.

Oliveira was chief of police in Carson City, Nev., and Phoenix was the lead patrol officer. When Oliveira moved up the BIA ranks, he recommended Phoenix for the chief's job and she was hired.

When Phoenix and Smart decided to come to Montana -- where Smart would take a career advancement -- Phoenix was hired as an officer at Lame Deer. Her goal was to become an agent and when a spot opened up, she earned the job.

"She has just done fantastic, which we knew she would," Pryor said.

When the BIA and Indian Health Services teamed up last year for a kids' camp, Smart and Phoenix were the first BIA police employees Pryor tapped to be mentors.

"They have that attraction," Pryor said. "People gravitate toward them because of their attitudes, their personalities."

If her friends find any solace in Phoenix's death, it is in their belief that she is with her children, Shasta and Justin.

"She missed them so much," Pryor said.

Shasta, 6, and Justin, 8, were killed along with Phoenix' brother, Ronald Phoenix, in a wreck in February 2000. They died after a man with a medical problem crossed the median on the Pyramid Highway and hit their pickup head-on.

Phoenix became an advocate for installing barriers on the median, which the state did.

She also fought to allow roadside memorial crosses when Nevada considered having them removed -- including the ones for her family.

Phoenix could have become reclusive after her children's deaths, but instead shifted her maternal instinct to caring for co-workers and the victims that BIA law enforcement serves, Pryor and Oliveira said.

"I can't think of a day she wasn't doing for someone else," Oliveira said.

She hosted the annual Shasta and Justin Youth Memorial Basketball Tournament in their honor.

The tournament grew to the point it "literally had too many teams," Oliveira said. Just as teams flocked to the event, people were drawn to Phoenix.

"She was like a celebrity," he said. "When people showed up, she was auntie. She was walking around holding kids and taking care of kids."

Oliveira said the Bible passage on John 15:13 best reminds him of Phoenix. "Greater love has no man than this, that a man lay down his life for his friends," Oliveira quoted.

"That is her," he said. "It's talking about devoting your life and giving your life. I think that's what she did, she devoted her life."