You have done a wonderful job bringing her around and you certainly look fine on her size wise. She looks very happy with her new home! I would offer a suggestion to move the nose piece up on the hack. It should be much higher up on her face. Where it's sitting now, when you put pressure on her reins you are putting pressure right above the the most sensitive part her nasal cavity plus it's sitting right on the soft tissue of the airway.
She looks great under saddle, very relaxed. And you are definitely not too big for her. With some riding (when you start), she will bulk up a bit on muscle and she still has some growing to do also. She may end up shooting up another hand before she's through. She is a very pretty girl and you are doing great!