"The fact she is on board now is down to how much closer the five of them have become recently."
The Wannabe hitmakers have grown closer this year in the wake of Mel B's bitter split from husband Stephen Belafonte - which saw her accuse him of being abusive and getting their nanny pregnant - in March, with Geri's baby son Monty, now 11 months, also said to have been a "uniting force".
The source added: "Things between them were quite icy at the start of the year.
"But gradually the ice thawed, and Mel was the one who drove that. Mel's divorce battle also helped to bring them back together, as did the birth of Geri's son.
"Plans at the moment are still in the early stages, and everything involving the girls tends to be complicated because they are so busy.
!It is not easy to get them all in the same place at the same time.
"But the team behind the reunion are delighted to have made it to this point."
The group are working with their former manager Simon Fuller on the reunion plans.
Geri, 45, recently teased that "bits and bobs" with the rest of the group were still being planned, after she gave up attempted for a reunion to mark their 20th anniversary.
She said: "I really pushed to get everyone back together. It got to the point where I just had to let it go.
"I still love the girls and there are other bits and bobs in the pipeline."
- Bang! Showbiz
