Is she who suckled with my sister considered my sister, given that I am older than my sister?

Whoever your mother nurses becomes your sister through nursing, whether she is older or younger than you, if the prohibitive suckling occurs with five separate feedings while she is under two years of age. In this case, she becomes a daughter to your mother and your mother's children become her siblings. As for someone who nursed with your sister from an unfamiliar woman, she is not considered unlawful for you, because the nursing of a child does not affect the rest of their siblings.