To demonstrate his power to Kirk, Kelvan leader Rojan ordered Hanar to reduce Thompson into a dehydrated porous cuboctahedron solid, the size of a Human fist, composed of Thompson's base minerals which represented the "distilled" essence of Thompson's being. Rojan crushed and crumbled the solid in his right hand, killing Thompson, leaving nothing but powdery dust remains on the ground.
After her death, Kirk found himself unable to get the image of her crushed remains out of his mind. (TOS: "By Any Other Name")
Thompson was played by actress Julie Cobb, who had the dubious distinction of being the first and only female redshirt to die in the classic series.
According to the script, her first name was "Leslie". She was credited simply as "Yeoman".