The Royle Family actress will finally make her Weatherfield arrival as Stella Price's mum Gloria in September.
The 68-year-old former Brookside star had her original first scenes cut after being taken ill last month.
A source said: "It's taken a bit of time to write Sue back in because the writers needed to find the perfect scenario to introduce her character."
The insider continued: "From the few days Sue was in before she fell ill, everyone was impressed at how wonderfully she fitted in."
Teasing her new opening storyline, the informant added: "The new scenario is even better than the first one."
Digital Spy confirmed earlier this month that Johnston would be returning to the Coronation Street set.
Producer Phil Collinson cast Johnston as Gloria Price back in April.