To be fair, the woman got a call right before Christmas from her daughter (after said daughter had a breakdown and threw up in a gas station to purge) confessing that she had an uncontrollable eating disorder and was fearful for her health and needed her family to get her help If her daughter is telling her that x, y, and z caused it and, as a mother, she's also heard other things proving such to be true, it makes sense she's angry. In the wild, mother animals rip out the throat of a potential danger to their children. Luke should be so lucky she's only dragging his name in the media.
And as a former addict herself with issues that may be buckling due to the stress of seeing her family fall to pieces and her daughter in a big mess of probable depression or other mental illness, she probably feels like a failure for not "protecting" her daughter or seeing the signs earlier.