The British girl band - also consisting of Cheryl Cole, Nicola Roberts and Kimberley Walsh - recently met as a five-piece for the first time since 2009 and things were initially frosty as Nadine and Sarah didn't feel part of the group.
A source told heat magazine: ''At first it was very frosty and awkward - particularly for Nadine, who hasn't seen most of the girls for over a year and has rarely called them.
''Cheryl was the first to break the ice, making a joke about what a rollercoaster few years it's been. After that the conversation started to flow. There were tears from Nadine who felt a bit cut off from the rest of the girls. Kimberley, Nicola and Cheryl have remained very close and Nadine and Sarah felt very much like the outsiders.''
The girls - who were formed on British reality TV show 'Popstars: The Rivals' in 2002 - have decided the reunion will go ahead but only as a five-piece.
The source continued: ''There had been talk that they might reunite without Nadine. She definitely feels like she's been blamed for the delay in the reunion, but actually it's her who wants it most. They do all agree that to come back it would have to be all five of them - or not at all.''
The girls last performed together in September 2009 and have since all gone onto to do their own things, with Cheryl becoming a solo star, Kimberley appearing in musical theatre, Nicola launching her own make-up range, Nadine moving to Los Angeles while Sarah recently spent time in rehab.