(Keizer, OR)  --  Authorities say a woman who was arrested after her four-year-old son died in a fire at a Keizer apartment was on probation at the time.  Niya  Sosa-Martinez is facing multiple charges, including manslaughter.  Prosecutors say Sosa-Martinez was under the influence of marijuana at the time of Friday's fire, in which the boy died of smoke inhalation.  Officials say Sosa-Martinez was on probation in connection with a previous conviction for second-degree child neglect in Woodburn more than two years ago.