The 17-year-old Gidey finished ahead of fellow Ethiopian Alemitu Hawi (21:00) and Dera Dida (21:01).
The leading French finisher behind no less than six Ethiopians was Aurore Guerin, who pipped European 10,000m silver medallist Clemence Calvin for the domestic honours in seventh place. They shared the same time of 21:35.
In the men’s 10.4km, 17-year-old Abadi Embaye – who can already boast a 5000m best of 13:13.17 – claimed victory in 30:36 ahead of Kenya’s Cornelius Kangogo (30:39) and Bahrain’s Birhanu Yemataw (30:41).