Missy was this way too. She's still very quiet. She only barks if she truly thinks there's a reason, such as if she hears something or someone out of the ordinary. Even then, it will only be a bark or 2 until I say "it's ok Missy".
I think every dog is just different. Our pug dog is a yapper. You'd think that Missy would have picked it up from her, but Nope. Thank goodness!