… The SheEOs, made up of female entrepreneurs who stepped off the corporate ladder to blaze their own trail, are a new breed. For Sarah Biller, who’s on her third start-up, Capital Market Exchange, being a SheEO allows her to strengthen her negotiation skills — including preparation and drive — in order to be more effective in a “testosterone heavy’’ environment. “In the world I operate in, you see a lot of tough negotiating and fist banging. It’s a great reminder to be in a group that understa …