Red Duck Can't Quack

Last year I was given a baby duck and raised her until we could find her a better home. She was named Kuzko and as a baby was yellow with a black spot on her head. She never learned to quack for some reason, just makes a hissing noise almost. She lost her down and turned completely white except for the black spot on her head still and she was really big (this is when she was a good 5 months old). We compared her to the other ducks on the property and she was almost twice as big, but not as large as the geese. We went to go visit her around Christmas time and she had gotten even bigger and her feathers on her face were red. Around her eyes were red, and around her beak as well as the beak itself was striped red. She still had the black spot on her head. The lady we gave her to thinks she's not fully a duck, but what I was wondering is if ducks are known to turn red, outgrow mallards and not quack. Please help - thanks.
-Jenn