"She works little in the office."
Translation:Ella trabaja poco en la oficina.
Ella trabaja UN poco = the amout of work she does may be small, but it's a possitive thing. Maybe she is part-time. Maybe she actually works a lot, but the speaker is downplaying it.
Ella trabaja poco = the amount she works is small, and it's definitely a negative thing. Maybe several times a day, she leaves for "a quick bathroom break" which takes 40 minutes every time because she swaps text messages with her friends.
At least in American English, we use "(verb) a little" and "(verb) little" exactly as Duolingo is teaching it in this lesson.
CindySue, I would beg to differ. Those actually have two slightly different connotations though they could be used to say basically the same thing. As an English speaker I have definitely said something similar to 'She works little...'.
As for the difference. 'She works little' tends to place more emphasis on the lack of work. In contrast, 'She works a little bit' places more emphasis on the actual work being done.