How many dogs do you have? Might it be a case that, in reality, she has bonded with the other dog/dogs rather than with you? And pup feels under pressure? Maybe some one-on-one time with her might help - short sessions of chasing a tennis ball, playing tug, feeding her from your hand etc, having a bit of fun, no pressure might bring her out of her shell? Is it a case that because the old dog was good at her job, you have become comfortable with that and maybe expect too much from the pup?