Saturday's concert, which was part of Liverpool's European Capital of Culture celebrations, saw Natasha Hamilton, Liz McLarnon and Jenny Frost play together for the first time since December 31, 2006.
The set included a cover of Cilla Black's 'Anyone Who Had A Heart', which is released on January 28.
Katona, who left the group in 2001, claimed she requested to be involved in the reunion, but was never contacted by the girls.
She told the Daily Star: "I got a call from the manager asking me if I wanted to be involved.
"I said yes, but then I never heard anything."
Singer Jenny Frost, who replaced Katona in 2001, commented: "All our friends came along."