stepsister
She is my stepsister.
Mary es mi hermanastra.
Mary is my stepsister.
Es mi hermanastra, pero para mí es mi hermana.
She's my stepsister, but to me, she's my sister.
En realidad, Susan es tu hermanastra.
Actually, Susan is your stepsister.
Mary es la hermanastra de Tom.
Mary is Tom’s stepsister.