Although the translation offered is exact, the sentence is incorrect in Dutch and English. "Two" demands a comparative and not a superlative. It would have to be "Van de twee meisjes is zij de jongere." and "Of the two girls, she is the younger (one)." (For some reason this post was censured. I should appreciate a reason why.)
Regarding your statement that the Dutch sentence is incorrect I can be short. It's not. In Dutch it's completely acceptable to use the superlative: http://ans.ruhosting.nl/e-ans/06/04/03/04/01/01/body.html
Regarding the English:
- "When there are just two members in a group, traditionally, we use the comparative. However, in informal situations people often use the superlative" (https://dictionary.cambridge.org/grammar/british-grammar/comparatives-and-superlatives/comparison-adjectives-bigger-biggest-more-interesting)
The discussion if the informal use is strictly incorrect etc. is something I'll stay out of. However, for the purposes of learning the superlative use in Dutch it serves its purpose here. Either way, for the ones that have a hard time using the superlative, younger is also accepted.
If I am going to have a guess on why your other post was removed, I would say probably because you simply stated that the sentence is wrong in Dutch. Personally I think it wouldn't hurt to have a little look yourself. Or another possibility is that it was an error/mistake.
how would you re-write this to ask the question "Of the two girls, is she the youngest?"