Mitchell (pictured), competing for Great Britain, finished fifth overall with 963 points.
She impressed in the swimming and the combined laser-run event, but she had given herself too much to do to claim a medal after being ranked 12th after the opening fencing discipline.
Mitchell’s swim time of 2:13.61 was the third best of the day.
Her college team-mate Kleidon, competing for Germany, finished just behind in sixth spot with 957 points.
Great Britain’s Olivia Green won gold with 1,032 points, ahead of Portugal’s Maria Migueis Teixeira (1,014) and GB’s Zoe Davison, who claimed bronze with 989.
The international event attracted top under-19 pentathletes from across Europe.