It seems that you are struggling w/ your IF and not being able to give your DD a sibling. I believe that there is a mourning process when someone moves to DE as to the loss of the genetic connection to your baby. However, you know you are ready to pursue DE when you want a child so bad to build your family and this is the best option to do so to bring a healthy child into the world. Let your heart guide you as when you are ready you will never think of one child as OE vs DE and the struggles that you mentioned in your post. All you will care about is the love you will have for another person and your DD will have a sibling to grow up with and this is what truly matters.
Keep trying w/ OE until you are successful and if not then listen to your heart.