Last week, Kelly announced her intention to bow out from her role as Becky McDonald at the end of the year. She will remain on screen until early 2012.
Following the actress's announcement, some reports suggested that Kelly had quit the soap amid rows over her character's storylines.
However, writing in her latest new! magazine column, Marsh commented: "I was disturbed by reports about my friend Katherine Kelly, who is leaving Corrie, that described her as a 'prima donna'. That's absolute nonsense - she's a lovely person. I think the papers pick on her sometimes.
"Of course she'll be missed but she wants to spread her wings and move on - which she's entitled to do. I don't think she'll be disappearing from our screens, though, as I expect she'll be popping up in loads of things."
Kelly has also insisted that her decision to leave Corrie was merely influenced by a desire to try new projects and spend more time with her loved ones.
She recently tweeted: "There are some nonsense stories out there today folks. Loved every minute of Corrie. Wouldn't change a thing."
Marsh, who plays Weatherfield's Michelle Connor, gave birth to a baby girl named Polly last month. She is expected to return to Corrie later this year.
Read the full story in this week's new! magazine - out today.