"I'm so excited because I'm going to wear a body suit," she told E!. "It will be from neck down so it will cut out time and the blisters."
A doctor had to be called to the set to treat her during filming of Matthew Vaughn's film.
The actress added that filming will begin around May.
"I haven't read the script yet," she said. "I haven't had 30 minutes. They literally gave me the script and I was like, 'I can't read this until Monday'."
I am so excited, I love X-Men and all the actors....
She will rejoin X-Men: First Class cast members James McAvoy, Michael Fassbender and Nicholas Hoult in the film.
Bryan Singer has also secured the return of Hugh Jackman, Ian McKellen, Patrick Stewart, Anna Paquin, Ellen Page and Shawn Ashmore from the previous trilogy, with Halle Berry "90% sure" that she will also be back.
Game of Thrones Peter Dinklage will star as one of the film's villains.