Why can't I use "seconde" instead of "deuxieme"?
you can, even if Duo did not list it as a correct answer.
Why is "La fille deuxieme est belle" rejected? Is it that belle is an overstatement?
I assume that the difference between "jolie" and "belle" should be the same as the one between pretty and beautiful.
Therefore it is not really an overstatement but probably a different set of criteria.