Yes, this sweet story: http://blog.duolingo.com/post/53207277316/a-duolingo-proposal
You are correct: "mia" is not implied in this sentence. Without "mia" it sounds "bureaucratic". You need to use the possessive (as in English) to make the sentence clear. Ex. "Compro fiori per la mamma": I'm talking to my brother, we have a common mother. But: "Compro fiori per la mia mamma", I'm talking to someone with whom I don't share a mother.
but I was translating the sentence from Italian into English. "Fiancée" is regularly used in English. when there's an accent error in Italian, Duolingo points it out, but doesn't disallow the response. the accent isn't required in English (American keyboards don't even have accents), so I was surprised to have my translation marked wrong.