stepsister, half-sister
Tom ha una sorellastra.
Tom has a stepsister.
I have a stepsister.
She’s my half-sister.
Thomas ha una sorellastra.
Thomas has a half-sister.
Era una sorellastra e non valeva molto neanche come metà.
She was a half-sister and not much of a half-sister either.
— Léon (1994)
Mary è la sorellastra di Tom.
Mary is Tom's stepsister.
Sami aveva una sorellastra.
Sami had a half-sister.