General Serving size - 1/4 to 1/2 cup pellets per 6 lb bunny
Recommended Nutritional Value
Fiber 18% minimum (20 -25% best)
Fat 1 - 2% max
Protein 12 - 14% max (long-haired breeds may need higher)
Calcium 1% max
Pellet bags usually has recommendations on the back according to size. So if you know her weight that's a good place to start. I know you're looking at vets but it's hard to be precise on food without knowing age or weight. Hopefully you can find one and they'll be able to help you there.