Thigh gap is about genetics... or being pretty underweight.
I don't remember where I read it but over the summer I read a peice about the thigh gap and how so many girls/young women were striving for it to the danger of their health.
It said that, except for in woman with a naturally wide pelvis structure, a thigh gap is only attainable when the person is thin enough that their body starts cannibalizing their muscles. Normal inner thigh muscles will prevent the thigh gap in most women.
Lowest Adult Weight: 202 ~ Oct 2012