The 21-year-old actress, who has been in the ITV1 soap since the age of 10, said leaving the show will help her transition to adulthood.
"When I'm acting, I like things to feel real, and I didn't like Rosie's bitchiness. I didn't enjoy playing that kind of character. She went through a phase of being such a catty girl. As an actress you do the best job you can, but I didn't enjoy it because it didn't feel real," Flanagan told the Sunday Mirror.
"I always said to myself that I was going to leave when I turned 21. For me, the show represents my childhood, and I just couldn't have properly become an adult if I hadn't left. I'm so grateful for the opportunities Corrie has given me, but I was in a bubble and the time is right for me to go.
"It finally feels as though I've left my childhood behind. People keep asking me what I'm going to do next, but I just want to enjoy being me and live for the moment for a while. I've been on Corrie since I was 10. It hasn't just been my job, it's been my whole life."
Flanagan added that she now wants to play a completely different character, such as a role in Downton Abbey or Juliet in Romeo and Juliet.
Rosie will bid farewell to Weatherfield on Friday when viewers see her break up with Jason Grimshaw (Ryan Thomas) to pursue her dream of becoming famous by moving to London for a dating show.