Marie Caro was apparently suffering from "enormous guilt" and took her own life earlier this month, Britain's Daily Mail reports, citing Swiss newspaper 20 Minutes.
Isabelle gained fame after her anorexia-ravaged body was featured in a shocking 2007 advertising campaign, and she died in November at age 28 after being admitted to a French hospital.
"[Marie] felt guilty for having put my daughter in the Bichat Hospital. My daughter did not want to go to that hospital," Isabelle's stepfather, Christian, said.
He had also said in a statement shortly after his stepdaughter's death that she'd died "from the successive consequences of negligence by the medical staff." He has since launched a legal complaint against the hospital, according to the Mail.
Isabelle's battle with anorexia was put on stark display in a fashion ad campaign by Italian photographer Oliviero Toscani in 2007. Caro's naked body was shown with her skeletal frame and facial bones protruding, and the images were splashed in newspapers and on billboards with the headline "No Anorexia."