The vet also competes in agility, and notes that agility dogs tend to be on the thin side because of the incredible amount of exercise they get.
Because she's small and not particularly big-boned (though certainly she's not delicate - look at that chest - photo taken at 14 months - she'll be 2 on March 1) the vet is satisfied with her current weight. I run her by the office through the back door every week or so to monitor her on their high class scale. She is in incredible condition, we took her to the beach and she ran with other dogs and in and out of the surf for almost four hours without showing any signs of fatigue (she did sleep well that night though!) And her coat is even better since we put her on a custom dog food.