Need to help my mom...

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My mom only eats one thing a day and shes been passing out and getting sick a lot lately but she refuses to see what she's doing wrong. She only weighs one more pound than I do, she looks better than anyone her age and we are at a healthy weight but she wants to lose more despite what everyone tells her. She criticizes her body and even my own. We both have the same body type, slender with curves, we are both lucky but she thinks of herself so badly. How do I help her? :(