Yvonne Freaney, 50, was cleared of murdering 11-year-old Glen but convicted of manslaughter on the grounds of diminished responsibility.
After strangling her son, who was autistic, the domestic violence victim – whose three other children were also disabled – then tried to commit suicide.
Yesterday at Cardiff Crown Court, she was given a three-year supervision order for killing Glen.
A judge agreed with psychiatrists that Freaney’s culpability was very low and she had acted out of sheer desperation.
Mr Justice Wyn Williams described the case as extremely sad and the most difficult he had dealt with. He agreed with the defence that sending Freaney to prison was not in her best interests – and she had effectively been in custody since her arrest more than two years ago.
He told her: “There can be no doubt that you absolutely devoted to your son.
“I found this sentencing the most difficult one I have ever undertaken.
“You had a personality disorder and suffered from a very severe abnormality of the mind.
“The series of events you went through would have been difficult for even a person of robust personality.
“Your culpability, in my judgment, was very low.”
Freaney and son Glen were staying at the Sky Plaza hotel in Rhoose, near Cardiff Airport, in May last year.
She had moved out of the family home in Penarth, Vale of the Glamorgan, and living in hotels for about a month before Glen was killed after a breakdown in her marriage.
The court heard she had suffered years of physical abuse by her husband Mark, a former RAF serviceman, whom she married in 1996.
Police were called several times to the family home after alleged domestic incidents of violence. Freaney was seen by doctors several times for injuries, but never pressed charges against her husband.
Days before she left the family home – described by police as a “pigsty” – for the last time, the court heard that Mr Freaney said to his wife: “Why don’t you just f*** off and kill yourself?”
On the day she killed Glen, she was found alive in the Sky Plaza Hotel room, despite injuries sustained trying to cut her wrists and taking an overdose.
As she was arrested, she told emergency services: “It’s funny. He was laughing when I was strangling him. That is when I knew he was happy.
“I had to do it because now no one can point fingers at him. My only regret is that I couldn’t end my own life.”
During her trial, the court heard that Glen communicated through a computer by tapping on symbols on the screen.
He suffered from severe autism and still wore nappies at the age of 11.
As well as being his main carer, Freaney also looked after her three other children – who suffered hyperactivity disorder, dyspraxia and Asperger’s syndrome – as well as her elderly mother.
A psychiatrist’s report prepared by Dr Tegwen Williams, which was read aloud in court, said Freaney previously tried to kill herself in the 1980s and, at the time of killing, Glen suffered from a personality disorder “at the top end of the scale”.
After her arrest, Freaney was detained at a secure mental health unit ahead of her trial before being remanded in custody.
Last month, a jury of seven men and five women decided she was suffering “extreme mental stress” at the time she strangled Glen with a coat belt, and cleared her of murder.
Defending barrister John Charles Rees QC said his client had never disputed killing Glen from the beginning and was a woman with no previous convictions.
He called the prospect of imposing an immediate prison term as a “pointless exercise” given that Freaney has “effectively been in custody” since being arrested – and would be out on licence within a few days or weeks.