From an article I read, the boy has threatened on multiple occasions to burn the house down with the family inside. The woman wasn't told about the boys mental issues when she adopted him, and if she knew the extent of his issues I doubt she would have adopted him in the first place.
As a former bulimic, she needs treatment. And if it is as bad as you say, she needs inpatient treatment in a psychiatric ward that deals with eating disorders. Please pass this list of treatment providers in MI along to her family http://www.edreferral.com/states/mi.html