Translation:The younger sister-in-law prays frequently at home.
Ah, yes. These relationship phrases sometimes cover more than one possible condition in the absence of contextual clues. Wahine 'opio, is the younger sister-in-law, just as kāne 'opio is the younger brother-in-law. The older brother-in-law would be kāne makua.
Consider that "wife" and "woman" both translate to wahine. "Husband" and "man" both translate to kāne.
Same words, different definitions.
"The young woman prays regularly in her house". This is a translation that I think carries the essence of this phrase. The reason why I choose "her house" over "at home" is because I like to use "kona" when I am designating that a thing belongs to a person. Like a "house". But, according to Duolingo, my answer is wrong. Maybe they are flagging my use of the word, "regularly". When I think of prayer, I think of it being done like clockwork. Pray when I get up, prayer when I eat 3 meals, prayer when I go to sleep. I would say it's more of a "regularly" scheduled prayer than a "frequent" prayer. Doesn't "pinepine" also mean "regularly"?
Wahine ʻōpio can mean "young woman", but as a family term it can also mean "younger sister-in-law".
rabelon gives a nice explanation here: https://forum.duolingo.com/comment/32617330?from_email=comment&comment_id=34838724