"Does your friend have a sister?"
Translation:Hat deine Freundin eine Schwester?
In English to German translation, it can be either "dein Freund" or "deine Freundin". In my case, I mistakenly wrote "deinen Freund", it was incorrect and the suggestion was "deine Freundin" which is confusing. But in this case, since both "dein Freund" and "deine Freundin" are both accepted, the problem is the misleading suggestion.
Assuming you're referring to translating German to English, the friend must be a female (die Freundin). Usually "Deine Freundin" implies girlfriend whereas a female friend would be "die Freundin von dir", but normally the context is clear and this "rule" is sqidgy. A huge problem with Duolingo is the context is never there.