Sarah died aged 39 after revealing last August that she had been diagnosed with breast cancer, which had spread to other parts of her body.
Derry’s Coyle shared several photos of her with Harding on her Instagram page and said that she hoped her friend now knew how much she was loved.
The singer wrote: “One week without you!! Thinking of you all day everyday & trying to imagine how your new journey is going.
“Please feel free to come visit me anytime. I know lots of people will want some Sarah spirit time so I can wait my turn.
“I hope you now know how much you are loved & how you impacted so many lives by being wholeheartedly yourself.
“Always an inspiration, always a shining light & always my friend!
Mother-of-one Nadine has previously said she was “absolutely devastated” by Harding’s death.
In a post on Instagram last week, she wrote: “I can’t think of words that could possibly express how I feel about this girl & what she means to me!!
“I know so many of you will be feeling this way.
“For now I’m sending so much love to you!”
Earlier this year Nadine recalled how her friendship with Harding had blossomed after a shaky start.
In Harding’s memoir, Hear Me Out, she penned a tribute chapter to her pal, saying she was ‘fortunate enough’ to have gotten to know all aspects of her personality and not just the party girl side.
Writing about the moment they first met during auditions for Popstars: The Rivals in 2002, Nadine said: “It was the bright blonde hair; the seemingly confident air she had. She was so bubbly and loud — you couldn’t have missed her if you tried.
“Growing up in a small town as I had, I’d never met anyone like Sarah before. Naturally, I just rolled my eyes and thought ‘oh my God; she’s going to be one of those attention-seeking stage-school nightmares’.
“When we both got to the final 10 and all ended up living in a house together, Sarah and I ended up sharing a room. This was where I very quickly saw a different side to her.
“Surprisingly reserved, Sarah is a deep thinker. In fact, she spent much of her time with her nose in a book. I noticed her language and vocabulary as well.
“When you were having a conversation with Sarah, she’d use all these long words and cleverly articulated sentences, unlike the rest of the girls in the house. It was such a surprise that this personality was hidden underneath all the overblown bravado.”
As time went on, Coyle and Harding became firm friends, bonding over a shared love of cooking.
They began going on nights out together but Coyle ‘couldn’t keep up with Sarah’s pace’ and Harding began making new friends, ‘more in tune with the hours she kept’.
“It was the start of a whole new era for Sarah,” added Coyle.
Despite being the younger of the two, Coyle said she was always there for Harding ‘in the way a big sister would’ because she knew she was ‘quite vulnerable’ and that she hated confrontation.
In her autobiography, Harding wrote about a special pre-Christmas night with Coyle and their Girls Aloud band-mates last year. She said that during the evening, there were ‘moments of hysterical laughter followed by tears’.
“At one point,” wrote Harding, “Nadine told me in no uncertain terms how much she cared about me: ‘You don’t understand Sarah. I love you.’
“It was partially fuelled by wine but I also knew in my heart that she meant every word she said.
“After everyone had gone, I sat up late into the night talking to Nadine while we ate cheese and biscuits.
“Okay, so it wasn’t like the nights of wild partying I did back in the day, but it was still very special.”
Former bandmate Nicola Roberts also paid tribute to Harding on Monday, saying the last week had been a “blur”.
She added: “I wanted to show appreciation for the lovely tributes to Sarah and outpouring of love we have received.“Also, acknowledgment for how Sarah’s passing has affected many people who are fighting this cruel disease.
“My heart is with you.”
Harding’s death was announced on Instagram by her mother Marie, who said her “beautiful” daughter was “a bright shining star”.
Earlier this year, Harding said she was told by a doctor that she would probably not be alive next Christmas.
Harding and Coyle found fame with Girls Aloud alongside Cheryl Cole, Nicola Roberts and Kimberley Walsh.Tags: