In portuguese, when you say "trarão vinho para a festa" you can understand both sentences: "to the party" and "for the party".
The preposition "para" can be related to the verb "trazer para a festa" = "bring to the party", or to the noun "vinho para a festa" = "wine for the party".
Since it is ambiguous, "for the party" should be accepted. I must confess I understood "for the party" (because "para" is closer to the noun)... but after fifty days of duolingo, I believe I understood how she thinks (so, I put the first one).
If you want to say "they will bring wine to the party" in portuguese, without doubts, you could say: "Eles trarão para a festa o vinho", but I must confess it is unusual.