Flights Due To Emergency

My son, who is attending college out of town, recently had to have emergency surgery.  I purchased a ticket through US Airways to get to his location.  I know that other airlines have policies about emergency flights at reduced rates or obtaining a reduced rate after the fact.  I was wondering what the policy is for US Airways and what I need to do to get a possible reduced rate or partial rebate for the flight?  I have a letter from the surgeon on her leeterhead with her signature stating that this was an emergency surgery.  Thank you.