The letter cut right to the point: Hawah Jackson’s lights would be turned off by the end of the month if she didn’t pay overdue utility bills totaling hundred of dollars. Jackson, a nurse at a rehabilitation hospital, said she didn’t have the money and worried how her 22-year-old severely disabled daughter, Binah, would cope if the power in their Dorchester home was shut off. “She can’t stay in the darkness,’’ Jackson said. Binah, who has autism and doesn’t speak, often calms herself by switching on all the lights in the middle of the night, her mother said. Jackson told Binah’s pediatrician about the impending crisis. He called a lawyer and within days, Jackson had sent a partial payment to the electric company, which acknowledged that because of her daughter’s disability it couldn’t legally stop providing electricity.