Sadie Sink plays Jean Elaine Grey in Spider-Man: Brand New Day, a movie that, surprisingly, sets the stage for Marvel Studios' upcoming X-Men reboot.
The movie reveals that the Department of Damage Control captured Sara Grey, who, in the MCU, has the same abilities as her sister, Jean. However, they're limited, as they can project their consciousness into another person's mind if it's less than 33 feet. Sara uses her powers to stop Jean from following, preventing the DODC from capturing her (their mother abandoned them when their powers manifested, leaving them in foster care).
This is revealed late in Spider-Man: Brand New Day, explaining Jean's role as an antagonist for a big chunk of the movie. She sees Spidey working with the DODC, and understandably perceives him as an enemy.
Similarly fooled by Bill Metzger into believing Jean is a threat, Spider-Man helps capture her, freeing the DODC to continue the experiments that they'd been conducting on Sara (who, along with the mysterious "VMax," Jean is searching for throughout this story). They want to replicate her mind-control abilities so they can use them for their own nefarious means.
The last Jean heard from her sister was a psychic message about the aforementioned VMax, leading her to believe it's somewhere Sara is being held or perhaps even a weapon created by Metzger and company.
As she's experimented on, Jean looks up and sees an air conditioning vent with a damaged label: "VENTMAX." The "ENT" has peeled away, meaning "V MAX" was the last thing Sara saw before she died. Realising the truth, combined with the DODC's experiments, unlocks Jean's full telepathic and telekinetic potential, bringing her more in line with the powerful mutant from the comics.
It's worth noting that Spider-Man: Brand New Day never uses the word "mutant," and, despite rumours to the contrary, Peter Parker is not one of them. Instead, his powers have evolved, with a surge of the spider hormones in his DNA permanently leaving him with organic webbing, enhanced Spider-Sense, and increased strength.
As for Jean, after Peter helps her realise what it means to be "special" and a hero—after allowing her to experience a touching exchange he had with Aunt May—she decides not to kill Metzger, saves Spider-Man's life, and leaves New York on a bus.
With Jean Grey's origin story explored, the stage is set for her to be recruited to Professor X's X-Men as one of the team's most powerful members. Her powers aren't exactly pink energy blasts; instead, they're portrayed in a fairly grounded manner, and given how dark Jean's past is, we have a feeling Jake Schreier's reboot will be more in line tonally with 2000's X-Men than, say, The Avengers.
As for the DODC, the organisation clearly has a vested interest in superpowered individuals and has even created weapons capable of stopping Spider-Man (before his powers evolved, at least). Now, all signs point to the group being behind the mutant-hunting Sentinels, likely front and centre in the Mutant Saga. Metzger, for example, is on the run, so it's easy to imagine his hatred for mutants fuelling his future actions.
"Spider-Man: Brand New Day is everything fans could want," we wrote in our review of the movie. "Emotional, hilarious, and heartfelt, it’s an action-packed love letter to the comics and one of Spidey’s best big-screen adventures. Spider-Man has never been more amazing."
Spider-Man: Brand New Day is now playing in theaters.