Oh really? She should stop saying this in interviews then!
Agreed. She claimed this back in 2021 on the A&E series, "Biography" which focused on the creation of "Grease". She later went on Instagram in 2022 and repeated this same claim adding pictures of herself dressed as "Sandy 1" and "Sandy 2".
However, Jim Jacobs refuted this in a 2021 Chicago Tribune article:
“Well,” says Jacobs, laughing, “I’ve known Donna since we went to Garvey grammar school. She was Donna Miller then, and I was a couple of years behind her. I think we also went to Bible camp together and she dated an older cousin of mine. But the model for Sandy? That just isn’t true.”
https://www.chicagotribune.com/2000/10/13/grease-comes-home/