"I calculate that for a woman of median height of 5'4" (1.63 m), a BMI of 29 corresponds to 277 lbs (126 Kg)"
You should use this calculator then:
http://www.nhlbisupport.com/bmi/bmicalc.htm
The BMI for the woman you describe would be 47.5.
A 5'4" person with a BMI of 29 would weigh in at 169 lbs.
The calculator does not state the formula it uses to calculate results.