Keep an eye on her, sounds like she might just still be loopy, sore, and out of sorts from the operation.
I know when I brought Stella home they said she may or may not need pain meds the first night, depending on how her body processes what they had given her. Sure enough, she was whimpering a bit and wouldn't move at all from her spot in her bed. I gave her pain meds later that night after she wouldn't eat (more than 12 hours after her surgery) and within an hour she was up and about long enough to scarf down a bowl of chicken and rice (wouldn't touch her kibble though) and drink some water. Then, she got cold and started shaking (her little ears were so cold!), so I wrapped her up in a soft towel like a little burrito, put her back in her bed, and she slept through the night.
Just keep an eye on her, sometimes it's hard to watch them go through it but you just have to do what you can. They bounce back fast though, the worst part is over
