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An Oregon mother who had a breakdown while caring for her autistic son and ailing husband allegedly threw the 6-year-old off a bridge and then called police to tell them, authorities and relatives said Tuesday.

Jillian Meredith McCabe, 34, of Seal Rock, Oregon, was arrested for the killing of her son London, police said. Authorities discovered the boy's body in the waters of Oregon's Yaquina Bay hours after McCabe called 911 late Monday.

On Tuesday afternoon, McCabe made a brief appearance in Lincoln County court — via video conference while wearing restrictive clothing to designed to keep her from hurting herself. A judge ordered her held on $1 million bail on charges of aggravated murder, murder and 1st and 2nd degree manslaughter. She did not enter a plea and the judge set a preliminary hearing in the case for Nov. 12.

In the past, McCabe had spoken and written of "pulling a Thelma and Louise" — a reference to the movie in which two women drive their car off a cliff — as a response to the stresses of her life.

"We're all devastated," Andrew McCabe, London's uncle, told NBC News. "London was a good kid. He loved hats. And his Dad."

“She took him for a walk and did what she did,” he added.

Jillian McCabe at hearing in Lincoln County Court, Oregon, on Nov. 4. She appeared via video conference. KGW

Relatives said the once-stable mother suffered a mental collapse in the face of incredible challenges: caring for a non-verbal and autistic child, a health crisis that left her husband fighting for his life, and the death of her father.

"Jillian really struggled with her mental health and I know she was just out of her mind when this happened," said Tanya McCabe, London's great-aunt, who led the family effort to obtain psychiatric services for her. She was discharged more than once from inpatient care, she said.

"It was terrible what we went through to get her the help she did get," she said. "We worked full-time to get her the services but obviously they weren't sufficient."

She declined to provide further details, citing privacy concerns. Oregon's state health agency said it could not comment on an individual patient's case.

Family members say Jillian sought treatment when she lived in Hood River about two years ago.

“We sought care on several occasions. Due to the limited options in the public health system, we were only able to get her into an outpatient facility in The Dalles,” brother-in-law Andy McCabe told NBC News Tuesday night. “It was a limited time allowed. And since they refused to admit her officially to an inpatient facility, she was released to us."

"I know she was just out of her mind when this happened."

Tanya McCabe said London's mother had expressed thoughts of harming herself but the family never imagined she would kill her son.

"Jillian was always so patient with him, and loving. She really had a lot of compassion for his condition. When he was screaming at the top of his lungs, which was the only way he could communicate, she didn't get upset at all. She would calmly comfort him, and I was amazed at how patient she was.

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"So this was shocking and heartbreaking."

The family's difficulties were chronicled extensively on social media, through YouTube, Facebook and Google Plus. The authenticity of those pages was confirmed to NBC News by Andrew McCabe.

On a fundraising website set up by family and friends, Jillian McCabe wrote that her husband Matt had been diagnosed with MS and had a mass in his brain stem — going from acting as "the sole breadwinner and provider to not" in a matter of two weeks.

She recounted how she rushed her husband to the emergency room, where nurses had said "they couldn't believe London was severely autistic — he was so well-behaved." The appeal linked to a now-defunct blog called "Autistic London."

"I am taking care of our son London and now Matt full-time," she wrote. "I am applying for any and all assistance available… I NEED YOUR HELP."

"I love my husband and he has taken care of myself and my son for years and years and now it's time for me to take the helm," she added. "I am scared and I am reaching out. I hope I am not coming across trashy or over-reactionary. I must explore every avenue to take care of my family right now."

In a YouTube video of Jillian McCabe posted by a family member, she expressed her appreciation for support and funds and donations as the family struggled with Matt's diagnosis and caring for London.

"You are making this experience livable — versus pulling a Thelma and Louise — which I've totally thought about," a tearful Jillian said with a little laugh. "I said it."

Matt McCabe's Facebook profile documented the devoted father's medical struggles and family life with London and Jillian. Early photos of a young London — who was diagnosed with severe autism in 2011, according to a post — give way to a smiling young boy sporting a variety of hats.

"It's absolutely a tragedy."

In blog posts penned by Matt McCabe, he hinted at family troubles.

"Some of you 'know' and some of you don’t. Jillian and I are living apart right now," he wrote on the blog. "Life happens. We are still 'together' but living apart. This has been very difficult, but life is unique, right?"

But in September, there were signs that the family situation was improving. A YouTube video posted online last month showed Matt, Jillian and London celebrating the boy's sixth birthday at a table surrounded by stuffed-animal party guests.

In the video — titled “London McCabe’s Sixth Birthday" — Jillian hugs the hat-clad London close as he eyes a candle-lit cupcake, then claps and cheers as he blows out the candle.

In September, Matt McCabe posted that his wife had moved back in, and the situation seemed to be improving.

"Jillian is living with us, too," he wrote. "London is pleased as punch. He lays on our laps and puts our hands together. Last night he made the 'mmmwha!' sound and gave his Mommy a kiss. Then he made the same sound and pushed our faces together. He’s all smiles."

London McCabe playing with a toy giraffe last November. “He liked big floppy hats and anything that was fuzzy," his uncle said. via Facebook

London's uncle said he was "really sweet, energetic and a handful."

“He liked big floppy hats and anything that was fuzzy. He liked the feel of soft fur and fleece. It was a comfort to him…It was a sensory thing. It was what he was able to latch onto when he was upset. It would calm him down," Andrew McCabe said.

“He had a lion that was his favorite. He liked it so much he wore it out – they had to buy him a new one because it was all worn out,” he added. “He liked the water. Ironically enough. He loved the beach. And he loved playing in the water."

London carried an iPad with him everywhere, using it for educational games and to watch YouTube. "He was very intuitive, very intelligent… just trapped in a mind and a body that couldn’t communicate," his uncle said.

Coast Guard spokesman Jonathan Klingenberg said London's body was recovered early Tuesday. He said a good Samaritan had called in after spotting a body from a restaurant and lounge at the Yaquina Bay Bridge, prompting the Coast Guard's 25-foot vessel and fire department to zero in on the location. "The fire department got there first and recovered the body," he told NBC News. "It's absolutely a tragedy."

The Newport Police Department said that Jillian McCabe had been located near the bridge and interviewed by detectives prior to the discovery of her son's body. She was then arrested.

Andrew McCabe said he hoped the tragedy would bring attention to the lack of help for the mentally ill.

"The state of health care in the country and the lack of prioritization that we have especially for our mentally ill is appalling. And its heartbreaking and unfortunately there’s tragic results when people don’t get the help they need," he said.

— with Gisele Lamarre