"She is the worst student."
Translation:Ela é a pior aluna.
No. Not a rule, but some expressions, for instance, "grande dia" (big day). In such sentence, if you change the order, you change the meaning.
- "Ele é um homem grande" = "he is a big/tall man"
- "Ele é um grande homem" = "he is a great man"
- "Ele é um garoto pobre" = "he is a poor boy"
- "Ele é um pobre garoto" = " he is a guy on a pitiful condition, not meaning about money..."
Most of the time, when the adjective comes before the noun, it is more emphatic and may include a metaphoric quality to the noun:
- "Uma velha amiga" = "a longtime friend"
- "Uma amiga velha" = "an old friend"
This is a feature that has come down to the Romance languages from Latin. An excellent discussion of the topic can be found here: http://www.ling.upenn.edu/NWAVE32/abs-pdf/callou-adj.pdf
I appreciate your detailed explanation on the general use but in this very case it doesn't appear to apply.
Otherwise, how would you translate 'aluna pior' if not as well as "worst student"? I mean do you also have to turn her into the most terrible one? I do not think so at all and that's why this wording should equally be accepted if not even preferred.