I haven't read all of the replies, but I just wanted to give you a word of encouragement. My first two babes would only take a 20 minute break in between feedings unless they were sleeping. I was told with my first that I HAD to supplement. I did, but only at night, and only that 4 oz. I was so stressed, and constantly feared my supply was low. Now, looking back, I don't believe it was. I would say, if you have the patience and time to nurse that baby often, nurse that baby often. As long as she is gaining weight and happy, you shouldn't worry. Also, I can't pump worth a darn either. Some women just don't pump well.
Oh! One more thing! My kids are so sweet and loving, and I am convinced it's because I nursed them when they wanted to nurse. They had a ton of physical closeness that first year of life, and now I'm so grateful I stuck it out. Take care!