Milá žena would be one
copy of my previous explanation: The problem here is English and how Duo handles the courses. NICE when you speak about people in English does not refer to their external beauty but rather internal. BUT if you say 'nice' about a car in english, it refers to what it looks like and can be translated as 'hezky'. So the word 'hezky/hezka' has both hints but in this case only one can be used.
I know that's not supposed to be like that but to my poor Spanish ears žena sounds like /že'na/ with the stress on the second syllable. That's weird because that usually happens to me when the second (or more generally non-first) syllable has a long vowel, but in this case, I hear it that way even with a short vowel.
Be aware that the stress and the wovel length are completely independent in Czech.
As for the manifestation of the Czech word stress, I suggest https://fonetika.ff.cuni.cz/en/czech-phonetics/
The acoustic manifestation of Czech lexical stress is very interesting. Unlike in many languages, the stressed syllable is not associated with typical signs of prominence. Unstressed syllables are often higher, louder and longer than stressed ones. More specifically, it seems to be the post-stressed syllable which tends to be, speaking strictly objectively (acoustically), more prominent. Research indicates that what is essential for the perception of stress in Czech is not the prominence of the stressed syllable but, rather, a specific trajectory of acoustic qualities throughout the stress group. This trajectory can be characterized as delayed rise, L*+H.