Jorja Halliday, who was from Portsmouth on England's south coast, developed flu-like symptoms, which prompted her to take a rapid antigen test, just four days before her death on Tuesday (local time).
The result was positive and she began isolating at home, but her condition quickly deteriorated.
Her family said she was prescribed antibiotics when she started struggling to eat due to a sore throat, The Guardian reported.
She was taken to Queen Alexandra Hospital in Hampshire, where she later died on Tuesday, after a doctor found her heart rate was double what it should have been.
“They realised how serious it was and I was still allowed to touch her, hold her hand, hug her and everything else. They did allow me that. I’m at the point where I can’t comprehend that it’s happened,” Jorja's 40-year-old mother, Tracey Halliday, said.
“They worked as well as I think they could medically, but were unable to save her.”
Ms Halliday said Jorja, who was described as "a talented kickboxer and an aspiring musician" according to PA Media, had been booked in to get the Covid vaccine on the same day she died.
Preliminary results reportedly indicated the teen had Covid myocarditis, which is heart inflammation caused by the virus.
"One of the registrars at the hospital was saying to me they seem to be seeing it in teenagers around that age, that Covid symptoms are causing inflammation in the body," Ms Halliday told the UK's Sky News.
"In Jorja's case it turned into inflammation of the heart and that's why when they put her on the ventilator her heart couldn't take the strain."
Teen remembered as ‘loving girl’
Ms Halliday said her daughter was a “loving girl” who always wanted to help others, according to The Guardian.
“It’s heart-wrenching because your kids are always meant to outlive you, and that’s the one thing I can’t get over,” she said.
Jorja’s cousin shared her grief on social media and took aim at Covid deniers.
“No words, my beautiful little cousin was 15,” her post began.
“She had her whole life ahead of her and there are still some that think the virus is non-existent! Try telling that to my family!”
She urged anyone on her Facebook friends list who didn’t believe Covid-19 was real to remove themselves.
“I have no time for your ignorance,” the cousin wrote.
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