Translation:Har hun en storebror?
I would warn anybody trying to learn Norwegian with this that if you said "Har hun en stor bror?" it would sound like "does she have a large brother", and not an older brother. I would most definitely use "storebror" unless of course you where asking if her brother is large (fat). Though I would advice against asking such a rude question.
I know this is not the intention of the sentence, but I'm wondering if you were concerned about whether 'she' has a large brother (whether he is older or younger), could you say 'Har hun en stor bror?', which in English would be exactly like the English prompt sentence.