Kennedy, who’s just eight years old, was recently rushed into hospital before doctors admitted her to intensive care, after she’d contracted the bug.
She’s more vulnerable due to her spinal muscular atrophy (SMA), a genetic condition that makes the muscles weaker and causes problems with movement.
Kennedy also suffers from breathing problems as a result of her condition.
Her twin brother, Karter, also had SMA and died just weeks after being diagnosed.
Now Kelsey, 20, has penned an emotional post on her Instagram Story to raise awareness of the condition, and update concerned followers on her baby sister.
“No one understands how proud i am of my baby sister!!” she wrote.
“Kids who have SMA Type I normally cannot even survive a common cold, as they can’t even swallow themselves & they have breathing problems as it is…but she is fighting off covid & sepsis…she is obviously very poorly, and its taking a lot of hard work of course, deep suctioning, constant cough assists, constant treatments all day long but shes not giving up…she is just unbelievable.
“Everyone still keep her in your thoughts & prayers please thank you all xxx.”
She continued: “Every year of Kennedys life she has been in intensive care from just a common cold, which always lead to pneumonia or other awful infections, many of those years she has been put on life support machine…Kennedy has always struggled in the winter & even before covid, we never had anyone in our house in the winter…
“…and every day on a normal day we have to wash our hands and change our outside clothes before we go in to see Kennedy…this was all before covid, so you can imagine how much we tried to protect her from getting covid, but somehow she did, and we’re all heartbroken she caught such a terrible virus as we know how much it’s going to harm her poor little body.”
Kelsey added: “She’s been through so much all her life and she’s only 8…we also lost my brother to SMA when he was just 4 months old.
“He stopped breathing in the middle of the night. This is why I want to raise awareness and need more people to fundraise for @sma_uk because people need to realise how awful this disease is and there are millions of babies going through the same thing…not just mine!
“And I want to help all those little babies too! To all the SMA families that follow me I send you all so much love and just want you all to know that you are real life heroes, never give up.
Kelsey previously thanked fans for an outpouring of support after she told Kennedy had been admitted to the ICU.
She also announced she wouldn’t be filming for TOWIE’s Christmas special.
“I do have to self isolate for 2 weeks now and have done a Covid test today for people asking and that does mean I will not be filming for the @TOWIE Christmas Ep,” she updated fans.