within 2 days she drinks seven 16 - ounce bottles of water
therefore the total volume of water she drinks - 7 x 16 = 112 ounces
she drinks a total of 112 ounces of water
she drinks the total volume in 4 servings
therefore 4 servings -- 112 ounces
then 1 serving - 112 / 4 = 28 ounces
she drinks 28 ounces of water in each serving