By an attack by Quicksilver and Scarlet Witch

The Brotherhood is attacking Xavier's school Jean fights against the attackers shutting them down with her telepathy. Until something hits her knocking her into a wall at superspeed she turns to see Pietro Maximoff she goes to attack him only to be hit with red energy she looks up to see his sister Wanda Maximoff. She fights both of the twins and she actually wins by accidentally exposing Wanda's bra making pietro close his eyes as Jean hits them with a blast forcing them to retreat.