Do not free feed! Loads of problems arise with free feeding...dog's food drive diminishes - makes training more difficult, contributes to obesity/overweight dogs, stools are less predictable, encourage picky eating...
4 cups??? That's a lot of food. Of course she is drinking a lot of water - Purina is not a high quality food and dehydrating so dogs drink a lot. Remember to feed in a sustained and steady manner...keep the pups very lean to minimize risks to developing joints.