Laura Daniels, 30, had been 'gravely' ill and her family confirmed their 'beautiful girl ' died in hospital on Monday.
Her parents Tony and Susan Witheridge announced their daughter's death in a statement: "Laura had been gravely ill and was being treated in hospital. Our hearts are broken, our lives are shattered once more.
"The pain of this loss is indescribable and out family very much need time and privacy during this unbearable time."
Laura Daniels died five years and one day after her 23-year-old sister was brutally murdered on the Thai island of Koh Tao. Miss Witheridge was killed along with fellow backpacker David Miller, 24, from Jersey.
Last month it was confirmed that Burmese migrants Zaw Lin and Wai Phyo who were convicted of their deaths would be executed after their appeals are thrown out by a court in Thailand.
The two men insisted they are innocent and claim an earlier admission was the result of being tortured. The pair's lawyers had claimed evidence and DNA in the case was mishandled.
The brutal circumstances of Miss Witheridge and Mr Miller's deaths shocked the world. Evidence from a Thai court and an inquiry in the UK revealed Miss Witheridge died from severe head injuries consistent with multiple blows from the blade of a hoe.
A Home Office pathologist, Dr Nat Cary, said there was evidence Miss Witheridge had been dragged and sexually assaulted.
The attack took place around 100 metres from the respective bungalows of Miss Witheridge and Mr Miller. Their naked bodies were found on a rocky area of beach by a group of workers the morning after the attack.
The Witheridge family's grief was made worse by trolls and even death threats.
In 2016, Laura herself revealed she was the target of death threats. She was also send photographs of the murder scene.
The family praised the work of police family liaison officers who helped them in the aftermath of Hannah's death. In 2016, Laura attended the Norfolk Safer Community Awards when a new award was presented in honour of Hannah to recognise the world of liaison workers.
A total of £17,000 was raised by an online donation page set up by Laura to help the family travel to Thailand and pay for an interpreter.
Writing on the page, she said: "The past year has thrown our lives into disarray, tarnished our trust in anything and everything and made us question humanity.
"On my darkest days, I think about the people who have thrown themselves out of planes, run significant distances and those who have sacrificed precious pounds from tight budgets to support us.
"It is in these selfless acts of kindness that I see reason to keep putting one foot in front of the other."