Updated at 7:30 p.m.

Rebecca McQueen thought her mother might have suffered a heart attack when she found the 80-year-old woman face down and not breathing in a hallway inside her Milwaukie-area apartment on Saturday.

Distraught at the discovery, she called 911 and attempted CPR, but knew it was already too late. She initially mistook the blood on her mother's chest for vomit.

It wasn't until Clackamas County sheriff's deputies arrived that a small hole was noticed in Donna McQueen's chest. Later, Rebecca McQueen said, her husband told her he overheard a detective say there was a bullet hole in the front window.

After midnight, Rebecca McQueen received a call from a Clackamas County detective telling her that 21-year-old Noelle St. John, who was staying in neighboring unit, had been arrested in the shooting. The grandmother of three appeared to be an unintended target, the daughter was told.

The 80-year-old had been living on her own at the Clackamas Trails Apartments for at least seven years and pushed back on the idea of leaving. She had told a friend a few days before the shooting that she would rather "die in my apartment with my cat" than be placed in an assisted living home, her daughter said.

"My mom had a community of people taking care of her so she could continue to live independently," Rebecca McQueen, 56, said Wednesday. "I was worried about her being too friendly and being taken advantage of. None of us ever thought this was something we'd have to protect her from."

St. John is now accused of first- and second-degree manslaughter and criminally negligent homicide. She was arraigned Monday in Clackamas County Circuit Court, but did not enter a plea. She is scheduled to appear for a preliminary hearing on July 5.

Donna McQueen was kind, outgoing and generous, her daughter said. She loved art and animals, and taught her two children and grandchildren to see beauty everywhere in the world. It wasn't uncommon for the woman to help strangers when she could, her daughter said.

According to a search warrant affidavit, St. John told investigators she and her boyfriend had been arguing Friday night inside his apartment. At some point, she said she grabbed his .380 caliber handgun from the night stand next to his bed, pointed it at her head, "being dramatic," the affidavit said.

The 21-year-old then said she opened the front door and fired one round outside around 11 p.m., the affidavit said. She claimed her boyfriend came out of his bedroom, asked what she had done and took the gun away from her. When she was questioned by deputies that night about the shooting, she said she told them that she heard the gunshot but didn't know where it came from.

The boyfriend's apartment is a third-floor unit near the center of the 306-unit complex. McQueen lived on a first-floor unit directly across the parking lot at least 100 feet away.

Investigators talked to several residents to determine the source of the shooting, according to the affidavit, but no one could definitively say where it came from.

Donna McQueen wasn't found until her daughter arrived sometime after 1:30 p.m. Saturday to take her to a relative's memorial service. One of the mother's friends who lives nearby used a spare key to open the locked front door, Rebecca McQueen said.

The 80-year-old appeared to have been in the middle of vacuuming in another room, her daughter said, but at some point went near the front window and was hit by the bullet.

According to the search warrant affidavit, St. John told investigators that she and her boyfriend went to bed after being questioned by police. St. John left Saturday morning and later that day got a call from her boyfriend that police were back at his apartment, the affidavit said. St. John said she took a cab back to the apartments that evening when her boyfriend wouldn't respond to texts. She met with a detective when she arrived, the affidavit said, and said she heard on the news that someone in the complex had been shot.

The boyfriend told investigators that St. John had lived with him until October but still visited regularly, the affidavit said. He said he was in another room when he heard the gunshot and that he put the gun and shell casing in a safe after St. John fired, the affidavit said.

According to the affidavit, police were called to his apartment in October after he claimed St. John threatened to harm herself with a knife. The boyfriend told police that he took a gun away from her on that occasion, too.

No one was arrested because a crime hadn't been committed, the affidavit said. It is not clear what actions were taken. Several neighbors told The Oregonian/OregonLive on Monday that St. John and her boyfriend had a volatile relationship and were often heard yelling at each other.

According to court records, St. John was arrested in Multnomah County in April on suspicion of driving under the influence of intoxicants and reckless driving. She reported to jail staff that she had previously been diagnosed with post-traumatic stress disorder, was in a psychiatric hospital at 13 and used Oxycodone daily.

Rebecca McQueen said she later learned that St. John and her daughter both attended Da Vinci Arts Middle School in Portland. The two are the same age, but didn't know each other well at the time.

McQueen said she holds St. John responsible for what happened, but doesn't blame her. After retiring in 2014 from the Multnomah County Corrections Department after 30 years as a probation officer, counselor and other roles, McQueen said she believes she's seen cases similar to St. John several times over.

"People talk about justice, but there's no justice here," McQueen said. "The person I'm angry at is the man who lives in that apartment and why he felt the need to have a gun. Why would you have that gun around with someone who is so obviously unstable as this young woman is? And everyone at the apartments knew it."

McQueen said she hopes to one day speak to St. John to tell her about her mother. She said she would like to tell her that if she ever needed help, she could have counted on knocking on her mom's door and being welcomed in.

-- Everton Bailey Jr.

ebailey@oregonian.com

503-221-8343; @EvertonBailey