Even she can do basic dressage. If you find a good dressage instructor who is willing to work with you and the horse (and not just teach what she always teaches) I am guessing you can get her using herself the best she can.
Anyways. I don't mean this to be mean, but were it me I would lunge the horse in side reins and/or pay someone to train the horse for a while and then you take lessons on an experienced horse that knows its job. As riders it is important we realize our limitations and take time to teach ourselves and the horse separately. It's like you're trying to teach the horse a piano lesson you haven't even learned yet. Even if you are only able to lunge the horse in side reins, do that for a week and every time after before you ride her. She needs to gain some understanding of what you want because right now she doesn't know. As far as once she in under saddle, rhythm, relaxation/suppleness and finally contact. Until you have the first two steps, you will not have the third.