What is making you doubt yourself? There are plenty of people with only 1 big mac, and the bird couldn't be happier. Have a look at Tabxo's threads, please.
Do you happen to have any pictures to share with us of Carmen and her setup?
I am the happy owner of a greenwing~ personally I couldn't imagine having another large bird, maybe a smaller one, one day~ My biggest fear is that we would lose "our" relationship
She is beautiful. If she seems happy and you are able to spend enough time with her, I think a friend is not really necessary. I would only consider another bird if you are prepared to give them the same amount of care and time. Just because you have two birds, it does not mean you have to spend as much time with them. 2 birds would mean twice as much time out of your day to spend with them and twice as much care. Just something to think about. Good luck in your decision!