Agreed. What indicates that 'they' are women? I have missed this one several times as I can't hear the female voice say nosotras and don't see any other indication in the sentence that it is women in the office (other than the female voice which is not a 'clue' in Duo. I appreciate that Duo does not discriminate in that way).
I overhear Spanish conversations all the time and Spanish speakers, where I live; speak very fast, run their vowels & words together and "muffle/swallow" certain sound combos. Listening on Duo has helped me decipher conversations in the real world. I'd recommend listening to the regular speed, then the slow speed, then the regular again. It helps you "hear" what's being said. After a while you won't have to follow that process, most of the time. It just takes some practice. Occasionally, there are spoken errors here, but not often.