Why is my answer wrong?: she presents the prince to the friends
I reported an error
A more appropriate answer would be "She introduces the prince to HER friends", since the word "dela" is presumed by the context, but it would probably be considered wrong by Duolingo. "To the friends" is, I believe, the less appropriate way.
They are likely to be her friends as you say but that isn't certain, so I believe Frencesca's answer should be accepted.
Jane and Bill, best friends forever, break into the palace where they meet the queen. She introduces the prince to the friends.
I also reported "the friends" as acceptable-to-be, just as Frencesca. Apart from the situation, "os amigos" means THE friends, so I guess it should be accepted as a good solution.
to her friends or to a general group of friends?
Probably to her friends
So I thought, so the standard translation should be "She introduces the prince to her friends"