Taking to Instagram, Walsh uploaded a black and white photo of the late star and said her passing “feels more real than ever”.
She penned: “Sarah passed away a year ago. I can still hardly believe it to be honest but it feels more real than ever today.
“Thinking of her always and of everyone who loved and miss her too,” followed by a broken-heart emoji.
In July, the remaining members of Girls Aloud - Nicola Roberts, Cheryl Tweedy, and Nadine Coyle, took part in a Race For Life event which aimed to raise money for charity Cancer Research UK in Harding’s memory.
“It doesn’t feel like she’s gone at all,” Tweedy said during the event as she reflected on how she has coped with Harding’s death.
“To be honest, I’ve never experienced or anticipated this grief. You know, I’ve lost grandparents when I was younger and I lost a friend when I was younger but nothing like this, the feeling of shock and disbelief and it still lingers now, to be honest.
“I still can’t quite believe it’s real,” she added.
Harding shared her cancer diagnosis on social media in August 2020, revealing that it had advanced to other parts of her body.