Amy Irving (Carrie) Carrie
Irving was De Palma's original choice for Carrie White
Amy Irving came into the joint De Palma-Lucas casting sessions as De Palma's preferred candidate for the lead role. She read well enough to be his first choice -- until Sissy Spacek's Vaseline-and-sailor-dress screen test made, in De Palma's words, "everyone else look silly." Irving was reassigned to Sue Snell, the guilt-driven girlfriend who engineers the prom date as atonement. (indiewire, wikipedia)
The demotion was a gift. Sue Snell is the film's most ambiguous character -- the one girl who stops throwing tampons and feels genuine remorse, but whose motives Collins and the audience are never fully sure about. Irving plays the ambiguity straight, never tipping the performance toward either reading.
Irving's real mother plays her screen mother in the final scene
In the epilogue, Sue's mother answers the phone and reports that Sue is "sleeping too much" but improving. The actress playing Mrs. Snell is Priscilla Pointer -- Amy Irving's actual mother. De Palma noted the documentary quality that real family relationships brought to the screen:
"There's something about mothers and daughters playing scenes that takes on a reality, like a documentary reality... the authenticity of twenty years of a relationship that's hard to manufacture." — Brian De Palma, Cinefantastique (1977)
The casting pays off in the film's final seconds. Mrs. Snell rushes in to hold Sue after the nightmare -- "It's all right. I'm here" -- and the comfort carries the weight of an actual mother-daughter bond. The Closing Image's emotional force depends partly on this reality: Sue's scream is answered by a real mother's arms.
Irving returned for the sequel and continued working with De Palma
Irving reprised the role of Sue Snell in The Rage: Carrie 2 (1999), the only original cast member to return. She also appeared in De Palma's The Fury (1978), playing another young person with telekinetic powers -- a film that explicitly continued the themes Carrie had established. The Fury casting suggests De Palma saw Irving as a natural fit for the specific register of vulnerable characters caught in supernatural forces. (wikipedia)