The five members of the group have not performed together since the closing ceremony of the 2012 London Olympics, a 2019 reunion going ahead without Victoria Beckham.
But Horner has told The Sunday Times "there will be something" with all five members involved.
"My hope is we come back together as a collective," she said.
"It's more respectful to come as one. We'll come as one."
Despite rumours of a falling out with fellow band member Melanie Brown, Horner said all five Spice Girls are in a group chat.
Horner, who releases her latest children's book series Rosie Frost: Ice On Fire in April, also scotched suggestions she had changed her surname to Halliwell-Horner.
Her marriage to Christian Horner, principal of the Red Bull Racing Formula One team, came under the spotlight when he was accused of inappropriate behaviour towards a female employee.
He was cleared by an internal investigation and after a subsequent appeal, but the story resurfaced in recent weeks when it was covered in the latest series of Netflix's Formula 1: Drive To Survive.
"We like playing games. We're quite silly," she said before dismissing the name change, saying Halliwell-Horner was her writing name.
"I haven't legally changed anything - Horner is the name on my passport."
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