Теперь цифры в ответах не принимаются. Только словами: https://www.duolingo.com/comment/13605072$comment_id=14316317
Sure. "She isn't fourteenth girl" isn't possible. "girl" needs an article: "She isn't the fourteenth girl" is fine. "She isn't a fourteenth girl" would technically be correct in some obscure situation but I can't think of any at the moment.
"She is the fourth from the right" and "She is fourth from the right" are both fine. "the" adds the extra level of definiteness. Whereas "She is a fourth from the right" is wrong. I believe that "fourth" is a noun in these sentences but it's clearly not behaving like a regular noun because it's a numeral.
Basically the rule would be if the ordinal is immediately followed by a noun then "the" is necessary, otherwise it is optional.
Thank you for your help. It's a little tricky for me. An adjective is clear case. Is it possible to say she's fourteenth girl. Could 'fourteenth' be a determiner of a noun or there's the only one possible option with 'the'. Another case: She is the fourth from the right and she's fourth from the right (the second sounds awful to my ears) By the way, the second or second)) Oh gosh. I'm getting more and more confused.