The introductory lesson "Final Hiragana: わ, を and ん" teaches the vocabulary "woman" spelled おんな and later on the beginner lesson "The Center of the Universe" says that おんな = female and おんなのひと = woman.
I looked up おんな in a dictionary and it can indeed mean female or woman. Is there any way to tell which word is meant? My assumption is in actual Japanese writing they would be differentiated by a kanji or context.
For the purposes of Nihongo Master dirlls however, おんな is both the right and wrong answer depending on what drill you happen to be on so it seems like a random guess.