Jean Grey was one of the founders of the original X-Men. She had natural telepathic and telekinetic powers and was a human host for the Phoenix Force, an ancient cosmic entity which granted her additional powers.
Cosmic Brick Crisis
Attack on the X-Mansion
Upon the X-Mansion being attacked by Magneto's forces, Jean Grey and Cyclops entered the school after putting out the fires on the X-Mansion's park, rescuing Stan Lee in the process. Upon entering the school and seeing the ensuing chaos, including a rampaging Juggernaut, the two focused on rescuing sets of students after Xavier instructed them via his psychic powers. Eventually, the two walked in on Storm fighting with Toad. Despite Toad initially having the upper hand, Storm was able to repel him and join the two. The three worked on evacuating students until the building was put into lockdown by Beast. After breaking through the door as per Beast's instructions, the three saw Iceman fighting with Pyro. After Iceman defeated Pyro, the four rescued the last remaining students, with Magneto then sending them a threatening video message. Taking the secret passageway to Cerebro, the four found Magneto and Mystique, disguised as Professor X, with the tesseract. Easily able to see through Mystique's disguise, Jean and Iceman pursued the two as they fled, while Cyclops and Storm went to take protect the students. As the two chased Magneto & Mystique, they were joined by Beast. Upon reaching the Hangar, however, the three were attacked by Juggernaut and a group of Acolytes as Magneto and Mystique fled. Jean Grey and Iceman used their powers to weaken Juggernaut before Beast removed Juggernaut's helmet, allowing Jean to control his mind, letting her and Iceman incapacitate Juggernaut and take him into custody. 
Jean to the Rescue
After Tony Stark, Thor Odinson and Peter Parker were abandoned in a sinking A.I.M. sub, Jean arrived to protect them, immersing them in a protective forcefield. The group made their way to a sub that Doctor Doom had stolen and was currently trapped on an ocean cliff, with the three protecting Jean from nearby Doombots. Reaching the sub and making their way inside, they confronted Doctor Doom, Thor knocking him out with Mjolnir and dislodging the ship in the process. Doom was not brought into S.H.I.E.L.D. custody, however, as Magneto then rescued him by controlling the Statue of Liberty. Breaking out of the Submarine, Jean went back to report to Xavier.
Searching for Recruits
After the Cosmic Brick Crisis was resolved, Jean went looking for new X-Men recruits with Wolverine at Fogwell's Gym, Logan found Blob, who proved to be uncooperative. Jean and Logan were able to subdue Blob with a mix of water and vegetables, which caused Blob to over-eat and exhaust himself.