All puppies vary in terms of rate of growth and development, so the question should be more whether she is the right weight for her. Workers particularly vary size wise - some weigh up to 20kg as adults, others less than half that. The size of both parents might give an indication of whether your pup will be a smaller cocker as an adult, but not always. So long as she is healthy, happy, eating well and not skinny or losing weight, I'd not worry.
