(covers information from several alternate timelines)
Kalara, formerly Jessica Wolff, was a Human female who served as a Federation Starfleet officer until she was stranded on the planet Altamid. Wolff became the alien Kalara after the use of energy transference technology severely mutated her body.
Wolff served as a sciences division Starfleet officer during the 22nd century, serving onboard the USS Franklin. In 2164, the Franklin was displaced by a wormhole while inside the Gagarin Radiation Belt. The ship crashed on the distant planet Altamid, with Captain Balthazar Edison, Anderson Le, and herself as the only survivors. (Star Trek Beyond)
Stranded on Altamid
On Altamid, Edison, Le, and Wolff found technology left behind by a previous civilization, including Swarm ships, a drone workforce, and an energy transference process that allowed her to "drain" other individuals to prolong her own life. Using their newly-acquired Swarm, Edison, Le, and Wolff captured scores of alien ships and drained their crews to survive, which also mutated their biology to resemble that of their victims. In time, Wolff became "Kalara", suppressing much of her Human identity and ceasing to speak in English. (Star Trek Beyond)
In 2263 of the alternate reality, Kalara was sent, in an escape pod, to the Federation Starbase Yorktown to pose as an alien in distress, as Krall wanted her to lure the USS Enterprise to Altamid. As part of that ruse, she claimed she had been in a ship whose crew was now stranded on the planet.
Searching for the Abronath
Though the Enterprise was subsequently attacked and destroyed by Krall's forces at Altamid, Kalara survived the ship's destruction aboard a Kelvin pod. She then joined Captain James T. Kirk and Ensign Pavel Chekov on the surface of Altamid, though Kirk realized she was complicit in the attack and became suspicious of her. Boarding the wreckage of the Enterprise's primary hull, Kalara hoped Kirk and Chekov would lead her to an artifact and weapon called the Abronath, but she was tricked by Kirk into sending a communications signal to Krall, thereby exposing his location on the planet.
Reinforced by several Swarm soldiers, Kalara engaged Kirk and Chekov in a firefight, but was waylaid by the Starfleet officers when they engaged the crippled Enterprise's thrusters and escaped back to the surface of Altamid. Managing to escape the ship herself, Kalara gave pursuit but was killed when the Enterprise saucer section, propelled by the firing thrusters, flipped and crushed her. (Star Trek Beyond)
"Do you believe every sad story you hear?"
- - Kalara and James T. Kirk, about Kalara's motives (Star Trek Beyond)
"What did Krall want with this thing?"
"To save you... from yourselves."
- - James T. Kirk and Kalara, about Krall wanting the Abronath (Star Trek Beyond)
The make-up for Kalara was designed by Joel Harlow. "Kalara was extremely difficult," he said, "because her face was so smooth. It had to be done in one piece – if I broke it anywhere you would see the edge. It was basically an entire face that had to be glued on." (Cinefex, No. 148, p. 85)
A pair of concept sketches of Kalara can be seen at TrekCore.