I wrote ο άνδρας της είναι άθεος and was marked wrong.
Nice sentence for learners: ο άντρας = the man, ο άντρας της = her husband
Make also this option to be correct:
Her man, not only her husband.
I wrote "Her husband is atheist" without indefinite article. The droid ood the article was accepted in similar sentences of this exercise, so I think it should be accepted here as well.