Are the measurements 36-27-39 too big for a 5'4 girl?

NO , It is not. I am the same measurements and height. My BMI is high because I am naturally muscular but once my body fat testing is done , I am considered very healthy. It really matters how you carry yourself and how much of it is fat. Those measurements in and of themselves are fine and you actually sound healthy because your not carrying your weight in your stomach, thats the only unhealthy place to carry extra fat. Hope this helped. If you are unsure go see a Doctor Who will do body fat testing.