Elizabeth is Frankenstein’s adopted sister and his wife. She is also a mother-figure: when Frankenstein’s real mother is dying, she says that Elizabeth “must supply my place.” Elizabeth fills many roles in Frankenstein’s life, so when the Monster kills her, Frankenstein is deprived of almost every form of female companionship at once.
Some critics consider Elizabeth a vague, unrealistic character who is far less developed than the male characters in the novel. One reason Elizabeth may seem insubstantial is that Frankenstein, the narrator, doesn’t see her very clearly. When he does see her, it’s as a possession: “I[…]looked upon Elizabeth as mine.” Elizabeth dies because at a crucial moment Frankenstein overlooks her entirely. The Monster tells him “I will be with you on your wedding night” but it doesn’t occur to Frankenstein that the Monster is threatening Elizabeth.