A 46-year-old woman who was reportedly undergoing treatment for breast cancer was beaten to death while she waited for a shuttle to take her to a Cancer Treatment Centers of America facility in Illinois, according to family members and local authorities.

Shannon Vincel of Springfield, Mo., had finished chemotherapy and was undergoing radiation at the center near Chicago, her family told the St. Louis Post-Dispatch.

Police said she was waiting outside a hospital residence one evening last week when a man walked up behind her and hit her over the head with an unknown object. She sustained a “severe head trauma” and was taken to a hospital, where she died the next day.

Her attacker got away.

“Our darling Shannon was taken from us suddenly,” Vincel’s obituary read. It added: “She will be remembered for her friendliness and happy smiling face.”

Vincel’s family members and friends are gathering Tuesday for her funeral in St. Louis.

“Shannon was so kind and she didn’t deserve this; no one deserves this,” her mother, Anita Adam, told CBS affiliate KMOV. “Being a cancer victim, for someone to deliberately take her life it’s unthinkable to me.”

Vincel had traveled from her home in Springfield to the cancer center in Zion, Ill., where she was scheduled to stay in the hospital’s temporary housing facility while undergoing treatment, according to the Post-Dispatch.

Vincel’s mother said the two spoke Aug. 15 after Vincel arrived at the temporary residence.

“I said, ‘but just be careful darling,’ ” Adam told KMOV. “She always closed with ‘I love you, Mom.’ That was the last thing I heard from her.”

“She certainly was looking forward to being Shannon again,” Adam told the Post-Dispatch. “She’d lost all her hair, but she dealt with it so well. She just accepted it: ‘This is what I’ve been dealt, I’m going to take care of it and get better.’ ”

“She was a girl unto herself.”

Cancer Treatment Centers of America at Midwestern Regional Medical Center in Zion, Ill. (Cancer Treatment Centers of America)

About 9:30 on the night of the attack, police said, Vincel and another person were sitting outside the residence, where Vincel was waiting for the shuttle. Police said a man wearing dark clothing walked up and struck her in the head.

“She thought she was in a safe area because it was on hospital grounds,” Adam told NBC affiliate KSDK, adding: “She was just sitting there waiting for the shuttle to pick her up and take her to treatment. Why would anyone just walk up and beat a girl from behind, without warning and just beat her to death? Why?”

Vincel died Aug. 16 and detectives started investigating the incident as a homicide, Zion police said in a statement.

A Cancer Treatment Centers of America spokeswoman said the facility has been working with the Zion Police Department and the Lake County Major Crimes Task Force during the investigation and has pledged a $25,000 reward for information leading to the arrest and conviction of Vincel’s killer.

“Our thoughts and prayers go out to the family and friends of the victim who, as has been publicly reported, was a patient at our hospital and involved in the tragic incident outside of Guest Quarters West, one of our hotel accommodations,” the spokeswoman said in a statement to The Washington Post.

The statement added that “security has always been our highest priority and in the wake of this incident, we have increased our security presence as a precautionary measure to protect the safety of our patients, guests and employees.”

Adam said she’s anxious for police to find the man who took her daughter’s life.

“He was just pure evil,” she told KSDK. “So it would be wonderful to get this — I can’t even call him a person; I don’t know what I can call him — if that thing were off the streets. Because no one is safe with people like that out walking around.”

“It’s broken my heart,” she added to the Post-Dispatch. “I can’t believe she’s gone.”

Read more:

Deadly and beautiful: The mesmerizing images of cancer research