Jo Whiley says her sister Frances "would like to say a huge thank you" to everybody who has helped her after she contracted coronavirus.
The broadcaster revealed last week that her sibling, who has learning disabilities and diabetes, was admitted to hospital with COVID-19 after an outbreak in her Northamptonshire care home.
Whiley says her family has now gone from "discussing palliative care" for her sister to "sitting on her favourite bench drinking cups of tea".
Whiley, 55, has previously said she was living through a "nightmare" as she questioned why she was offered the vaccine before her 53-year-old sister, who has the rare Cri du Chat genetic syndrome.
On Tuesday, Whiley posted a video of Frances giving a thumbs-up and a round of applause, and said her sister "would like to say a huge thank you to everybody who has helped her, especially the amazing doctors and nurses of the NHS, and her many MANY well-wishers".
Whiley also offered an update on her sibling's condition, writing on Twitter: "It's hard to believe we've gone from discussing palliative care on Friday night to sitting on her favourite bench drinking cups of tea."
But she added: "COVID has brought with it further complications.
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"We're now dealing with worrying diabetes and high blood pressure issues, and my parents are exhausted beyond belief.
"It's so hard observing from behind a visor and mask, helpless doesn't cover it."
She also renewed her call for people with learning disabilities to be prioritised in the vaccine rollout.
"Not everyone has been as lucky as us," she said.
"So many have died or are suffering from long COVID because they were simply not protected.
"We need to show them that they are not forgotten and we care."
Whiley had described it as the "worst week" of her life following Frances's diagnosis.