The actress, who plays Rosie Webster, has taken a three-month break from the ITV1 soap, during which she has cut her hair short and dyed it blonde.
She had claimed that show bosses were fine with the new look, but they have apparently requested that she reverts to her old brunette hairstyle before she returns to Coronation Street next month.
"They've said they don't want such a huge change for the character. It'll take her hours at the hairdresser - she's gutted," a source told the News of the World.
Speaking of the change last month, Flanagan said: "I've always wanted to be blonde, so I'll be keeping it like this for a while. Of course work knew I was doing it. Rosie is a model, so when she comes back, she'll have a totally new image. It gives her a more edgy look."
Flanagan recently signed a new 12-month contract with Coronation Street worth £70,000 and will apparently star in her own online spinoff. Get the Inside Soap magazine on your iPhone or iPad