The 24-year-old singer - who was the last original member of the girl group - quit the band last week and it has now been claimed she felt she had to leave because of the way Heidi Range and Amelle Berrabah were treating her.
The pair are said to have been envious of Keisha, 24, because she was the only member allowed to co-write their songs.
A source told Britain's Daily Mirror newspaper: "The girls were jealous as Keisha would meet up with writers, including Cathy Dennis, without them to create some of their biggest hits.
"When they had meetings with their management there was a perception Keisha was the only Sugababe worth dealing with. In some instances producers refused to start any work in the studio unless Keisha had arrived."
Keisha has now been replaced with former UK Eurovision entrant Jade Ewen, who has already recorded the group's video for new single 'About a Girl' and is currently in the US re-recording Keisha's vocal parts on upcoming album 'Sweet 7'.
Since Keisha's departure, Heidi and Amelle have both complained they felt bullied by their former bandmate and lived in fear of her mood swings and outbursts.
Heidi said: "It suddenly came to a head. Me and Amelle knew we couldn't move forward together the way it was.
"We couldn't work together anymore. But we did not want to throw away what we had achieved and split up."
Amelle said: "Keisha didn't leave off her own back - me and Heidi couldn't carry on. You shouldn't have to go to work treading on eggshells.
"Heidi completely supported me and knew what was going on within the band. We weren't happy and it was a struggle to come into work."