It doesn't say "ένα κοτόπουλο" which would be "a chicken" it simply says "μαγειρεύει κοτόπουλο" so it is: "She cooks (or is cooking) chicken."
When you have an issue with a sentence you should make a Report. Here's how:
Go to the bottom of the exercise page where you'll see REPORT Click on that:
Then choose what you want to REPORT: (You'll see these to choose from.)
-The audio does not sound correct.
-The dictionary hints on hover are wrong or missing.
-The Greek sentence is unnatural or has an error.
-The "Correct solution" is unnatural or has an error.
-My answer should be accepted. This is the one you should click on if your translation was not accepted.
After choosing the REPORT you want to make you should post on the comment page.
Also use these tips to help you:
TIPS TO MAKE LEARNING EASIER + HOW TO REPORT A PROBLEM
And check out the Greek Forum here with more links.