That's the word-by-word equivalent. I'm asking how the language is used in practice. "The sister is planting flowers" is much more likely to be a sentence about a nun than someone being referred to via a kinship relationship.
Other language don't use possessives for family members as much as English does. I'm trying to understand if Swahili is one of them or not, or does Duolingo just have lots and lots of sentences about family members that actually aren't that natural. Most Americans at least don't refer to their sister just with "sister," so "Sister is planting flowers" is also likely about a nun.