Sandrelli was born in Viareggio, Tuscany, into a middle-class family, the daughter of Florida and Otello Sandrelli (who died when she was eight years old), owners of a pension in Viareggio.
Sandrelli naceu na Toscana nunha familia de clase media, filla de Florida e Otello Sandrelli (que morreu cando ela tiña oito anos), propietarios dunha coñecida pensión en Viareggio.