She doesn't appear in the novel and she is only vaguely mentioned with her father. They both approve Sue's behaviour regarding Carrie.
1976 movieEditEleanor Snell is played by Priscilla Pointer in Carrie (1976).
Eleanor Snell is the mother of Sue "Susan" Snell. She knows about the fanaticism of Carrie White's mother, yet tries to be as gentle as possible to avoid confrontation with her. She is married and has two children. Sue is her oldest child. After the prom disaster she takes special care of her daughter, but it only helps partially.
She doesn't appear in the movie.
2013 movieEditEleanor Snell is played by Cynthia Preston in Carrie (2013).
Eleanor Snell is the mother of Sue Snell. She is her only child. She likes the dresses Margaret makes. It is implied, she lives alone and that her husband Mr. Snell either died or she is divorced.
In the alternate ending she takes special care of her daughter, who is going to have Tommy's child. In this case it really helps her, but not completely.