I think she means that she is a being that is "greater" than her thigh width; however that is a very niche perception. Like most of you I read it as a fat person saying "thicker than thighs" stating that she is drastically fat. She is such a fatty she had to have a permanent mark on her body as a warning to others that she is exceptionally fat. She's so fat and ignorant she branded herself to make others aware she is fat and ignorant. It is either the incredible self-awareness or incredible self-delusion.