A Dorchester husband and wife are accused of defrauding the state’s Medicaid program out of $18,000 by using a relative’s treatment as a cover to file false claims — even after she died, Attorney General Maura Healey announced yesterday.Theodore Gilbert, 54, and his wife, Madeline Garcia Gilbert, 51, were indicted Monday by a Suffolk grand jury on one count each of Medicaid false claims and larceny over $250, Healey said in a statement.The couple is expected to be arraigned in Suffolk Superior Court on April 23.