"The train station is empty."
Translation:תחנת הרכבת ריקה.
This is not an answer, but an agreement of sorts - I was also marked wrong for including היא, and I too don't always know when to include a pronoun as a copula or not. Is there a rule or is it just a matter of common usage? If the latter, perhaps it should not be marked wrong when included.
A brief comment on a detail of this really brilliant and excellent course (for which I feel more than grateful):
This word תחנת is an example of one that is being used in exercises before any audio for it has been presented. Even now I am not yet sure what the vowels are, so I would submit that this is a kind of minor pedagogic 'bug' which is popping up at various points in the material.
(I would be learning the word with more confidence and delight if I had actually heard it, or knew what, phonologically, I was typing :-)