My 54", 50# Wing T-Bird is braced at 8-1/4" and shoots as fast as many of the custom bows on the market today. I can't imagine why yours isn't performing well. The T-Bird is one of the best performing bows that Wing Archery made.
By the way, you are measuring the brace height correctly (throat of grip to string).
If your draw length is close to 28" I'd recommend 1916s with 125 gr. field points if you shoot aluminums, or 50#-55# woodies with 125 gr. up front. I don't know anything about carbons, so I can't make a recommendation.
Hope ya get her shooting well. Let us know how things turn out.