Penny isn't sad. She's still recovering from the operation. It's okay to feel how you feel. I felt a twinge of sadness knowing that my female cat Esper would never have a litter of her own. She too is loving and adorable.
But in my own heart, I knew that I wasn't interested in breeding. There are too many kittens already in the world without loving homes. I don't want to add to that, nor do I want to reduce the chance of a homeless kitten from being adopted from a shelter.
Things will be back to normal soon. And by the time the fur grows back, you wouldn't be able to guess that she even went in for the surgery.