Steffie died from sepsis due to infected pressure ulcers, very low body weight and poor nutritional status, a pathologist found.
Her ground-floor bedroom was in an “appalling” state, in contrast to the clean condition of the rest of the home in Pandy, Wrexham county, Jones said.
Steffie’s parents, who gave no comment in police interviews, were initially charged with gross negligence manslaughter.
Guilty pleas of causing or allowing their daughter’s death were accepted earlier this year.
In sentencing the couple, the judge Mrs Justice Stacey said that Bernita and Alan Davies had “not loved or cared for ” their daughter and were both criminally responsible for her death.
She said she hoped their other daughter would be able to remember the “happy times”, dancing to Abba together, her sister’s success at college and the happiness she brought her sister when she lived at home.
“You were both well able to visit the doctor and get help for your own problems,” the judge said, but never sought help for Steffie as “she became more and more withdrawn and her horizons narrowed”.
“Your daughter said you let her fade away…it was so much worse than that” she said.
She said: “There is no evidence of her ever having been shown love and affection.
“Instead, she was verbally abused by you and you showed complete indifference to her suffering.”
The last time Steffie was seen outside the house, in 2017, her mother was seen shouting at her and calling her “stupid”, the court heard.
Alan Davies, a factory worker, told paramedics his daughter had not been out of bed for 12 months before she died and her younger brother said in December 2022 Steffie was bed-bound and too weak to open a box of chocolates he had given her for Christmas.
The judge said Steffie did not have underlying health problems before her death, adding: “It was you, her parents, you were the problem.”