I agree with what JBun said. When I feel like my rabbits had a bit too much of calcium I give a lot of leafy greens which are poor in calcium and rich in water for a few days to help to 'flush it out' (romaine lettuce, batavia, celery... Jerusalem artichoke and carrots - the roots! the tops are full of calcium - are also low on the calcium scale). If it's occasional, that there is nothing else than the white on the pellets and that she isn't straining to pee there is nothing to worry about.