Great news!
The lack of appetite is normal. The body is loaded with all sorts of drugs and the trauma doesn't help. This and the heart lung machine take a toll. Some of us have a lot of trouble sleeping, there are sometimes visual problems some lose their appetite, most have some memory problems and unfortunately for my wife - some of us turn into big whiny babies.
It can take a while for things to get back to normal. Even a couple of months post-surgery, some of them will still pester us.
Don't worry too much, but please encourage her to keep eating. It's important to keep her strength up so she can heal.
She's very lucky to have such a close family that cares about her. After a good attitude, having a good support system is everything in my opinion.
Kev