Perfectionism is a trying master. Howlerkarma's suggestions are completely on point. I would add one further approach if I were in your shoes: ensuring that your daughter sees you and your husband verbalizing a healthy acceptance of imperfection in your own achievements-- and failures. Being conscious of your own thought process and modelling healthy self-talk for your daughter will be a tremendous help for her in recalibrating her definition of success as an intrinsic reward.
I would also caution you to be scrupulous in minimizing the ways in which your encouragement could be misconstrued. For example, at my grade 10 or 11 graduation, I didn't have the highest average, though I won most of the subject awards in my courses. I recall my father being indignant at the process (on my behalf, at being so close) and interpreting his comment as disapproval. In reality, the top GPA holder took none of the hard math or science courses, which I so enjoyed, and my dad disliked that GPA was blind to course difficulty and diversity. I didn't understand his motivations at the time. Fortunately, I'm not prone to extreme perfectionism, so I was "just" hurt that he let a perceived failure overshadow many successes.
