sorry to hear about your poor girl.
Mikischo is right ....you must keep her hydrated. I woudn't worry about any food for now.
I always thought the vet kept a dog hospitalized for a couple of days after surgery for pyometra. Is there redness around the incision or is it leaking?
Is there any way you can contact your vet for advice? Dr. Lee does not log on every day but he will answer as soon as he does since he has received two pm's.