The actress - set to bow out as Rovers Return landlady Liz McDonald in the New Year - recently filmed scenes in Albert Square's Queen Vic for Children In Need special East Street, which saw the residents of Weatherfield descend on Walford and vice versa.
Among the humorous moments featured in East Street was the surprise 'revelation' that Liz is the biological mother of Walford favourite Kat Moon (Jessie Wallace).
Speaking to The Mirror, Callard explained: "I loved working with Jessie Wallace - I adore her. It was hard not to get the giggles. We were shooting a piece of history. I felt honoured."
Asked whether she would sign up for a Walford stint for real, she replied: "I could not say no. I'd give it a go - just for a while. I'd love to go back and play Kat's mum."
Callard announced her decision to leave Coronation Street in October, and Liz's departure is expected to air in the early part of 2011.
Discussing what is in store, Callard said: "My exit is fantastic. I don't die so Liz will be back. After I handed my notice in, I didn't know if they were going to kill Liz off or not, but they said they would like me to come back. I agonised over leaving because I love Coronation Street. But I want to go on stage and I have exciting plans."
> Callard promises "massive" Corrie plot