|Katherine (The Radical) (1975) [Katherine Alman]: Killed in an explosion when her own bomb goes off prematurely as she's planting it. (Thanks to Robert)
Carrie (1976) [Carrie White]: Bleeds to death after being stabbed in the back by Piper Laurie. As she dies, her telekinetic powers cause the house to fall in on her.
Verna: USO Girl (1978) [Verna Vane]: Killed in an explosion when the jeep she's riding in goes over a mine; we see the explosion, followed by a shot of her helmet in the wreckage. (Thanks to Shadrach)
The Man with Two Brains (1983) [Anne Uumellmahaye]: Playing the voice of a disembodied brain kept alive in David Warner's laboratory, her body was killed (off-screen) some time before her first appearance, by Merv Griffin injecting her with window cleaner. Her brain is eventually transplanted into Kathleen Turner's body. (Thanks to PortsGuy)
'Night, Mother (1986) [Jessie Cates]: Commits suicide (off-screen) by shooting herself; we only hear the shot and do not see her body. (Thanks to Anastasia)