Emma Frost had Mister Sinister, Doctor Nemesis and Fabian Cortez operate on her in order to boost her telepathic powers, and then making the world forget that mutants existed.
Knowing Emma, the thought of mutilating her body is abhorrent, but she went and did it anyway to save the mutants.
From – Uncanny X-men Vol. 5 #21
In my head canon, this is what happened in the MCU.