That's cute!I have three indoor ducks and I don't think its animal cruelty. I do agree with burrill and get some duck diapers. This way they can wonder all over the apartment as they please. As for personality disorders, mine are super sweet, except when they're hungry of course, then they turn into hungry hungry hippos! They still love being picked up and love to watch movies with me. Then even tolerate me when I have the urge to do something like this to them:
Nonetheless, I think ducks make great pets, just as a cat or dog would.
To the OP, it sounds like your duck has a great life! I don't see how anyone could call what you described "cruelty." I wouldn't worry about it. Ducks do get lonely if they're by themselves, but you're with your duck most of the time, so I'm sure she's fine. She has you as a companion instead of another duck.