I think it's the English word order that made your answer marked wrong. I am not 100% sure though. I hope this helps.
We can say "She is quietly drinking her milk." / "She quietly drinks her milk."
"She is drinking her milk quietly." / "She drinks her milk quietly."
**or if what she is drinking is not specified then you could say
"She quietly drinks."
"She drinks quietly"
You use "zij" when you want to stress that she or they did it. Use "ze" when you don't need to stress who it was.
- "Ze eet de appel" - "She is eating the apple" (an unremarkable statement)
- "Zij eet de appel" - "She is eating the apple" (not someone else)
Can anyone confirm this? Because I read on another thread that says definite noun is preceded in the word order before the adverb. But why the default answer in this exercise not following that rule? Thank you.