well, you can see the rest of her lower left leg and you can work out your thigh measurement from there. and judging from the left leg and seeing how the right thigh is thicker than it's lower part, the left thigh should be relatively the same size as the right one.

and like the other one that got flagged. this one artwork not meant to be entirely anatomically correct and don't have to be one. this is more into stylized and exaggerated approach.