Some vets will give an injection just after surgery and nothing sent home...others will send medication home so you should ask for it as it seems your dog is very sensitive to pain.
Watch her breathing most of all...if she's panting alot and not able to comfortably settle down/rest, then you know she's in pain. Its not recommended to give aspirin in this situation because its a blood-thinner and not recommended following surgery! She needs Tramadol or Rimadyl or similar, for the first day or two at home.
