"Her dogs are incredible."
Translation:Hundene hennes er utrolige.
Because 'sine' can only be used in the object of a sentence. ''Hundene hennes'' is the subject of this sentence.
I put "Hundene hennes er fantastik", and it was marked correct, with a note saying, "You had a typo in your answer" and saying I should have used "untrolig" instead. Surely that's more than a typo!
I did this too. I think the English synonyms here are both really close translations, making both answers correct. Though I think it's important to keep them apart for vocabulary reasons.