my wife is 5'3 105 lbs small or extra...
my wife is 5'3 105 lbs small or extra small
Focus more on the hip and bust measurements. We got a small for mom over the holidays. She's shorter than your wife and just a bit heavier. The small fit well except some tightness in the hips.
i am 5'4 and 117#. i am longwaisted with broader shoulders and long arms. the extra small fits me to a T.