Customer smashes the agents finger while closing the trunk of a car?

i work at a car rental agency,i was walking around a car with a customer to make sure the car was ok,she sounded a little upset because she did not get the car she waned although it was the similar car and we do not promise make and model, she was upset,and slammed the trunk and my thumb got crushed ,she did not seem very apologetic,said sorry once and left with the car, my thumb is swollen and my hand hurts,i cannot even fold the thumb.what can i do.