Why the n' ?

Question

Elle avait fait ses devoirs avant qu'il n'arrive.

Accepted Answer

Hi Marilyn,
I suspect that you have yet to come across this aspect of more advanced grammar.
Have a look here -- I think it will explain all for you.
Avant que + ne explétif + Le Subjonctif = Before I do
 
Hope it helps.
Jim

Answer

Jim is correct: this is a case of the ne-explétif, an advanced grammatical concept. It is not a negation because the second part of it is lacking (usually pas, jamais, plus, personne, etc.). Instead, it is used as a stylistic element, mandatory in higher level French and often dropped in colloquial French. You'll get to it in time.