Your absolutely fine on her, as has been said lengthen you leathers. Ours still growing at 6yrs supposed to be full up 14.2hh at moment 15.1hh!!! Enjoy her good horses are hard to find.
Mine was a bit deficient in front at 5. By the time he was 8 he'd filled out - shoulders were wider, neck had developed and now there is LOADS in front of me. Yours is still a youngster and will fill out no doubt. You look fine on her