Sandy is Sodapop Curtis's ex-girlfriend.
History
Sodapop told Ponyboy he was sure he was going to marry Sandy. However, when she got pregnant, she left to go live with her grandmother in Florida.
Soda later runs off, saying he hates being in the middle of his brothers' fighting, and it makes him feel more worse because she left him, and he loved her so much. When running out of the house Soda drops a letter he had written to Sandy returned and unopened which just broke Soda's heart more causing him to be in the bad mood he was in. She is mentioned once in the film, but Sodapop never says she moved or got pregnant.
Appearance
She‘s described by Ponyboy to have blonde hair, and big blue eyes that would look so happy every time she was with Soda (even though she didn't love him as much as he thought she did).
She doesn't appear in the movie (except in a deleted prologue).
Personality
Not much is known about Sandy, except that she is a greaser girl. Ponyboy thought she loved Sodapop with all her heart, but then Soda says she didn't love him as much as he loved her, because he wanted to marry her pregnant or not, but she just left him. She’s also not committed, because she had conceived the child with someone else, cheating on Soda.
The Gang
She would go out with Soda along with Steve and his girl on many occasions. She has met Ponyboy, because he knows what she looks like and what her personality is like. It is unknown if she had met Two-Bit, Darry, Johnny and Dally, or if they had all hung out.
Child
It has been stated whether or not Sodapop was the father of her baby. When he is explaining what happened to her, Darry gives clues that imply it wasn't Soda's: "When Sandy went to Florida… it wasn't Soda, Ponyboy. He told me he loved her, but I guess she didn't love him the way he thought she did, because it wasn't him."
She indeed cheated on Soda and got pregnant with someone else. Soda wanted to marry her, and help care for the baby, but she told him to stay away from her, moving to Florida to live with her grandparents. The baby was born in Florida in the 1960s.
Notes
Sandy was portrayed by Lynne Hatheway in the film, but her scenes were deleted.