According to The Sun, Buena telephoned Donaghy and Buchanan in a bid to convince both to reform the girl group's original 1998 lineup.
A friend of Donaghy told the newspaper: "She met up with Mutya for the first time in ages over the summer and they got on well.
"Now Mutya is convinced the original three could be huge again. She was on the phone all last weekend trying to convince the girls to reform. Siobhan's considering it."
A source close to Buchanan added: "Mutya is very keen to do this. Keisha has her solo career on the go - including recording with new star Jay Sean - but she feels more comfortable as part of a band.
"There were arguments in the past, but all three realise it was because they were young, headstrong and finding fame hard to cope with."
Donaghy left Sugababes in 2001 and was replaced by Heidi Range. Amelle Berrabah joined the group following Buena's exit in 2005.
Buchanan, the then sole remaining founding member, was replaced by former Eurovision singer Jade Ewen last month.