Kimberley also reveals in her new autobiography that a "wedge" developed between Nadine and the rest of the girl band and that they felt "sucker punched" when she hired her own manager in 2009.
Speaking about the band's dynamics, Kimberley says: "Nicola, Cheryl and I have always remained close in Girls Aloud, I think we'd have been friends even if we weren't in a band together.
"But I'm not sure that would have been the case for me with Nadine or even Sarah. That's not to say I don't care about them or respect them. They're just very different from me and I don't always understand where they're coming from."
Kimberley's forthcoming book, A Whole Lot Of History, has been serialised in The Sun. In it, she also speaks about last year's 'Ten' reunion tour, which saw the girls reunite for their 10-year anniversary.
"By the time we got to the actual shows, some of the old problems and niggles we had with Nadine started bubbling to the surface again," Kimberley writes.
After their last night in concert, Girls Aloud announced their split, saying: "Your love and support will stay with us forever but we have now come to the end of our incredible time together. Love you lots."
Following the announcement, Nadine tweeted her fans insisting she did not want the band to split, adding that she "had no part in it".
Kimberley, however, claims that Nadine had "never said any such thing to the rest of us, and splitting up was what we'd always planned".
Since they decision to go their separate ways, Nadine has revealed she is pregnant with her first child.
Now living in Los Angeles, Nadine has shared a cute picture of the baby clothes she has already bought her unborn son or daughter, adding that it's like "a really great dream".
Kimberley's book is released on 26 September priced at £20. Nadine and Sarah have stayed silent on Twitter about Kimberley's comments.
Were you sad when Girls Aloud split? Tell us below, as the best comment from across the website each week wins £50!