Call duck doesn't quack

[Diamond88]

My three-month-old, female call duck doesn't quack. From what I'd read, I imagined that a female call duck would be terribly loud! But my duck still just peeps like a baby. Every once in a while she'll let out a single, short quack when she's stressed--like when I walk away too quickly or when she tries to fly and falls off the couch. Other than those rare, single quacks though, she only peeps. Could it be that she never learned how to quack, since she's never been around other ducks? I'm planning on getting her a baby sister when call ducks start hatching again next spring, but so far, she's an only child so she's not familiar with the sound of quacking...although I assume it's an instinct and not something learned. And I'm sure she's a female because she's been both vent sexed and DNA sexed by vets, so it's not that she's a quieter male. She's definitely talkative, peeping all the time. She just doesn't quack. Any idea why that could be?