Gemma Sheehan is an ex-MMA champion. She teaches girls how to fight.             Deep social conditioning might have led you to reread the first two sentences. I don’t blame you. When I told my sister I was going to interview a former MMA fighter she smiled and asked, “What’s his name?” As a society, we have long internalized a cultural narrative that does not associate girl with fighter— certainly not of the punches-and-kicks variety.             The good news is that, according to Sheehan, this is changing.             “It’s why I started Girls Who Fight,” she tells me, referring to the business she founded nearly two years ago. “I noticed that…