Awww, bless her heart
I'd just keep an eye on her and spoil her a little with some plain lowfat yogurt, low sodium chicken broth, anything she really loves. If at any time you feel that she's not feeling better, give the vet a call. Her gums should be dark pink and not sticky to the touch. I'm sure by tomorrow she'll be feeling much better.
I wonder why the vet didn't give you pain meds for her? She had surgery, she's in pain and should have meds for that
Could be why she's not eating/drinking enough.