The 25-year-old 'Insatiable' star, who has failed to find the same success as Cole, said that it will be up to Cheryl to decide whether or not a reunion happens.
'Cheryl's success is a point for all the rest of us to consider from our own points of view,' she told i-D Magazine.
'We've got to be realistic about what has happened to Cheryl over the last couple of years.'
Another factor could be money - Coyle admitted that their hair budget alone went 'through the roof'.
She added, 'The money that would need to be invested in it is another factor.
'Between the five of us the hair budget alone was enough to feed a small country. It was through the roof.
'I think we bought our hairdresser an entire extension on the back of her house on one album campaign. If she wasn't driving a Bentley then she should have been.'