Hi there -- If the flu vaccine was the live type (nasal spray) it could pose a risk of infection with the virus (although a serious bout would be unlikely); If your daughter recieved the killed vaccine (injection) the prednisone won't render the vaccine useless and shouldn't cause any other problems either. Steroids merely suppress the immune system, which is all the more reason to be vaccinated, but only with the injectable (killed virus) vaccine. If your daughter received the nasal spray version and is still feeling fine she's already passed the test and this should confer the expected protection from H1N1 despite having had prednisone recently.
Hope this is helpful. Good luck to you both and please follow up with us here as needed.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist