It seems to me like you have a very considerate girl who cares about you a lot. She has laid her feelings out on the table, and seems to have her priorities straight.
She proved to you that she really cares about you because she is waiting until she can truly focus on the relationship, instead of agreeing to be with you and tossing you to the side.
Keep Seeing Her
Now on to your question, you should continue to see her because you both seem to truly care about each other. If she is considerate enough ask you to wait until the timing is better, you should be considerate enough to wait for her.
But I do think that while you are waiting you may see other people, just make sure that they understand that it can never be serious. If you care about her as strongly as you say you do, I doubt that your feelings will fade just because you see other people.
My advice really depends on how much you care about her, where you are in your life, and what your intentions are. If you aren't ready to seriously commit, still trying to be a bachelor, and have lukewarm feelings for her...then move on.
According to what I sense in your letter, this isn't the case. Remember the saying "love is patient, love is kind."