For a simple sentence to describe a noun with an adjective, it would be Uʻi kēlā wahine. Beautiful (is) the woman. That is a complete thought. Otherwise, the adjective follows the noun 99% of the time. The words kēlā wahine u‘i just mean "that beautiful woman", which is just a phrase instead of a complete sentence.
So "u'i" was used for the sentence "The farmer is handsome". So why is "The woman is handsome" marked incorrect? It could be either "handsome" or "pretty" and I've heard of a "handsome woman" used in conversation. I think that "handsome" should also be accepted as correct in this case. Thanks.