I've decided to clarify why BellaDona was neutered.
Bella is now (2013) 11 months old, she was never prenant and she never received any contraceptive.
In the morning, I've noticed that Bella feels slightly under the mood and it seemd that her belly is painful to touch. She had a discharge, so we went to visit our veterinary doctor.
The doctor did the basic check-up and considering all results (sono: enlarged uterus, 55k LEU) he diagnosed Bella with pyometra. After that, it was about me making decision what treatment (conservative or surgery) to pursue.
I did some research and apparently the conservative treatment is quite painful for cats and there is not any guarantee they will get well. My first rule is that the health of the adult cats I have is much more important than the number of litters or kittens.
With the heart heavy with sorrow I decided for surgery, i.e. removal of the inflamed uterus.
A few days had passed and Bella feels great -- she plays fetch again and insists on being cuddled. And I know for sure she will never contract this disease again.
I don't regret my decision -- I just regret the possibility seeing Bella's offspring around. I'm considering keeping her with us and maybe take her to shows now and then -- she loved the attention, people loved her and I was happy that Bella is simply my Bella