Sharon Stone revealed some time ago that she had what she called a "wee role" in an upcoming Marvel film. Since then, few details of her character, or in which film she might appear have been revealed.
Now, according to an AARP profile on Stone, she says her character has "heat powers" and is a "superhero." This leaves a few possibilites for women with fire or heat powers in the Marvel Universe. Looking at what Marvel has planned for Phase 3 and beyond, Stone could be playing a version of the pyrokinetic S.W.O.R.D. leader Abigail Brand.
Brand was introduced in Astonishing X-Men, meaning her rights may be in contention between Marvel and Fox, but she's currently a supporting character in Captain Marvel, and has often served as the liaison between Marvel's cosmic wing, and its earthbound heroes. It's not inconceivable that Stone could portray the green-haired Brand in 2018's Captain Marvel.
As a bonus? She was created by Avengers and Avengers: Age of Ultron director Joss Whedon with John Cassaday.