Shocking evidence heard by Mold Crown Court told how Kaylea Titford, 16, was found in soiled clothing and bed linen, following her death at the family home in Newtown, in October 2020.
She weighed 22st 13lb, with a BMI of 70, at the time of her death, the trial at Mold Crown Court heard.
Her mother, Sarah Lloyd-Jones, 39, pleaded guilty to manslaughter by gross negligence last year but her father, Alun Titford, denied the offence, along with an alternative charge of causing or allowing the death of a child.
The court heard that Kaylea, who had spina bifida and used a wheelchair, died after suffering inflammation and infection from ulceration, arising from obesity and immobility.
Emergency service workers, who were called to the house after she was found on October 10, described feeling sick due to a "rotting" smell in her room.
Following the verdict, Powys County Council said "a concise child practice review" will be carried out, involving "all relevant agencies".
NSPCC Cymru assistant director Tracey Holdsworth spoke out after the jury found Titford guilty, saying the case showed the importance of safeguarding measures – and that a review was vital to make sure no child suffers in the same way.
She said: "Research shows that young people with disabilities are three times more at risk of abuse, and while Kaylea's parents are to blame for her death this case shows why having effective safeguarding systems in place across our communities is crucial.
"A child safeguarding practice review must leave no stone unturned in establishing what more could have been done to protect Kaylea and, crucially, ensure that other children do not suffer such appalling neglect unnoticed."