If she won't sit without treats, then its too early - she has not fully learned the behavior. Do yourself and your puppy a favor and get yourself to a training class! Especially if you've never had one before, since there are things a trainer can explain to you in person that a book never could tell you as effectively.

Look around at different schools - prices vary tremendously and ask what type of training they do. Their philosphies vary greatly too. Go to the one which sounds like it would fit your beliefs best. Lastly, inquire how many dogs are in any given class. I hear a lot of my students complain they joined a class and were one of 16 dogs. They felt lost in the crowd and didn't learn much because the poor trainer had their hands full.