NBC News - An Oregon mother who blogged about the struggle to care for her autistic son allegedly threw the 6-year-old off a bridge and then called police to tell them, authorities said Tuesday.

Police said that Jillian Meredith McCabe, 34, of Seal Rock, Oregon, had been arrested for the murder of her son London. Authorities discovered the boy's body in the waters of Oregon's Yaquina Bay hours after McCabe called 911 late Monday night.

"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.

He said it was unclear what happened in the hours before the tragedy, but the mother was coping with a series of 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.

"It's been a really tough year," said Tanya McCabe, London's great-aunt.

Still, she said, the family never imagined that the stressful situation would leave the boy in harm's way.

"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.

"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.

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 give way to a smiling young boy sporting a variety of hats — the kind his uncle said he loved.

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."

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 subsequently arrested for aggravated murder, murder and 1st degree manslaughter, according to police. Bail was set at $750,000.