Erin Martinez never got too involved in politics until her husband and brother were killed in an explosion after natural gas leaked from an abandoned line near her property. Two years later, the 41-year old high-school science teacher has become one of the leading voices calling for tougher regulations on this state’s booming drilling industry. Not far from where Ms. Martinez lives on the plains in northern Colorado, oil-and-gas wells have provided vital revenue for Lynn Fagerberg’s onion farm amid the uncertainty…