I'm no expert, but I think dogs can go a day or two without food. And I definitely wouldn't feed her in the middle of the night. You mentioned it's 1:00 a.m. there. It's important she has water, though. Just let her be comfortable. Make sure the surgical area doesn't look infected. Call your vet if it does. And help her get outside to relieve herself whenever you think it's been a long enough interval. Let her have a stress-free environment. If she had one of those time-release kind of pain medications before she left the vet's, she's not having it too hard. Maybe tomorrow spoil her with just a little soft, yummy food she's not usually allowed -- but not more than a few spoonfuls to make sure she can keep it down for a couple hours.
I'm a big advocate of healthy foods for dogs, not the chemical-laden stuff at the big box stores. So just take my input with a grain of salt. I'm a bit overboard on pets.