Carmen Davila was a civilian engineer attached to the Melona IV colony. In 2368, she was killed by the Crystalline Entity when it destroyed the colony for all the biomatter on the planet, while trying to save an elderly man who had fallen while trying to evacuate to underground caverns with the rest of the Melona colonists.
Commander Riker was asked by Captain Picard to write a letter to her family, following the colony's evacuation. (TNG: "Silicon Avatar")