JEFFERSON CITY, Mo. — A lawyer for a Missouri mother who says a pawn shop should be held accountable for selling her mentally ill daughter the gun she used to kill her own father challenged a claim that state and federal law protects the seller from liability.Attorney Jonathan Lowy, of the Brady Center to Prevent Gun Violence, told state Supreme Court judges Wednesday that Odessa Gun & Pawn was negligent when it sold Colby Sue Weathers the gun in June 2012, hours before she used it to shoot and kill her father …