The blue 1987 Chevy Nova was wedged in brambles on three sides off of 12th Street NE.
The car couldn't be seen from the road. Nor could the property owners spot it from their house. It took the eyes of a Snohomish County Search and Rescue helicopter pilot on Tuesday to find it.
"It appeared the car was backed in," said Shari Ireton, a sheriff's office spokeswoman.
Her family on Wednesday expressed relief that she had been found.
O'Neil was 89 and was in the early stages of dementia.
Her ordeal represents the worst fears for many families with an aging parent with dementia or Alzheimer's disease, which affects more than 5 million Americans. Research shows that 60 percent will wander and get lost at one point or another, said Becca Verda, a spokeswoman for the Alzheimer's Association of Western and Central Washington chapter.
Time is critical when they do roam. If not found within 24 hours, up to half will suffer injury or death, according to the Alzheimer's Association.
While the Snohomish County Medical Examiner has yet to determine the cause of death, O'Neil's disappearance provided a reminder of the importance of tracking bracelets for vulnerable people. It also kindled discussion about whether the state has an effective public notification system when someone with dementia or Alzheimer's goes missing.
Local search and rescue volunteers have long advocated that people living with Alzheimer's or other conditions, such as autism or traumatic brain injuries, sign up for Project Care Track, which provides traceable bracelets to people who are prone to wander.
The bracelets are outfitted with transmitters that send out unique signals that can be tracked by search and rescue teams. A receiver tuned in to the person's bracelet beeps louder as it gets closer to its location.
The signal can lead searchers to a lost person within minutes, not hours. The program costs $15 a month. Donations are available to those in need.
When Rodman Reynolds learned about O'Neil's disappearance in mid-July, the Everett man couldn't help but think about his own mother in Texas and the importance of an effective statewide public notification system.
His mom has Alzheimer's-advanced dementia and in 2012 vanished two times in six months. In one instance, she was found slumped over in her car that was out of gas and had a dead battery, about 160 miles from her home.
Reynolds said he is glad to know she lives in a state with a Silver Alert public notification system. Similar to Amber Alerts for abducted children, the Silver Alert gets the word out quickly to media when people with dementia, Alzheimer's, developmental disabilities or other medical disabilities goes missing.
Washington has the "Endangered Missing Person Advisory Plan" for people believed to be in danger because of age, health or mental or physical disability.
To date, it has been an underused system, Washington State Patrol spokesman Bob Calkins said.
"We have some educating to do, including with law enforcement and the public," he said. "We are not at all shy about admitting we have more work to do."
So far this year, it has been used 10 times for a variety of situations, including elderly dementia patients. That's a significant increase from the past, he said. Previous years' numbers were not immediately available.
State Sen. Barbara Bailey has sponsored legislation in the past to include a Silver Alert system in Washington state. These days, she is open to using the existing system if it can be made more effective in cases of Alzheimer's.
Just as an Amber Alert seems to convey the urgency of finding an abducted child, Bailey believes Silver Alert would quickly register in peoples' minds the image of a confused wandering adult with Alzheimer's.
"You want the general public to not have to stop and think: What does that mean?" she said.
Bailey's own mother suffered from the disease. There would be times her mother would wake up in the middle of the night and think she needed to get somewhere.
"When you have Alzheimer's people who are wandering, hours and minutes matter," Bailey said. "They are far more frail. They are far more suspectable to the environment."
Calkins said better training should lead to more agencies using the existing state-wide alert system.
O'Neil vanished July 16. She'd decided go shopping at the Everett Mall, just a three-mile drive from her home.
She was last seen in the 6700 block of 88th Place in Marysville, asking for a map and directions back to Everett. Everett police led the effort to find her and worked closely with several agencies, including Snohomish County Search and Rescue staff and volunteers and the Washington State Patrol's aviation unit.
O'Neil's family was thankful Wednesday that she had been found.
"The bottom line is we have some closure," said her son, Patrick O'Neil, of Olympia.
"She had a good life," he added. "She was a great lady and she had a heart of gold."