The Local Government and Social Care Ombudsman (LGO) ruled the council caused the family avoidable distress with delayed service reopenings after the first coronavirus lockdown.
The LGO has ordered the council to apologise to the family and pay £500 to the daughter and £250 each to her mother and father in damages.
A council spokesperson said: “We acknowledge the findings of the report but for confidentiality reasons, we’re unable to comment further.”
The LGO’s investigator found the council’s slow reopening of services last year meant the woman was unable to go to the charity run centre she visited four days a week.
She later received welfare check in visits but during one in September she complained about her arm and refused to use it which the ruling stated showed she was stressed.
The woman, who has a moderate learning disability and autistic traits, was on a council care plan which also included one visit a week to one of the authority’s centres.
Her family had a £14,772.60 annual allowance covering the visits, as well as a personal assistant for eight hours a week and 28 days of residential care a year.
The investigator ruled the council was not at fault for preventing users from visiting more than one day centre for coronavirus reasons once they reopened following the first lockdown.
The investigator also found the council was not at fault for not paying for a clinician to work with the daughter and for refusing direct payments to her father to cover care costs.
But they ruled the council was slow to start planning the reopening of day centres, with users’ families sent a questionnaire asking about their needs in July after lockdown ended.
The LGO ruled the council could have started planning reopenings earlier and noted it did not have meetings with providers until September or ask for risk assessments until October.
The investigator also ruled the council’s claim it could not force the charity centre to reopen was misleading because the authority’s records showed it decided how it would resume services.
The ruling stated: “The council should have taken these actions much sooner. That was the fault by the council which unnecessarily delayed [the daughter’s] return to the charity day centre.
“Were it not for the council’s faults, this should have been possible by September at the latest. This caused her avoidable distress and affected her mental health and left her parents meeting most of her care needs.”