Initially a close friend of the German Jewish art collector and editor of Das Kunstblatt, Paul Westheim, she later betrayed him.
The exact nature of her actions regarding Westheim's art collection has been the subject of much controversy, generating lawsuits, book and articles and speculation as to her motivations.
Weidler's correspondence with the Carnegie is considered to provide "unique insight and detail about the situation of artists in Nazi Germany" and that her exchanges with Carnegie president Homer St. Gaudens are "an extraordinary source of information for provenance researchers about the location of artwork pre-war and the changing attitude towards modern art in Germany as the Nazis rose to power.".
[16] Weidler also claimed that the famous German Jewish dealer Alfred Flechtheim bequeathed paintings to her, but this assertion was also contested in several lawsuits.
[20][21] The Grosz family criticized Weidler's account as false, submitting evidence that the paintings had transited through a Dutch auction house Mak Van Waay known for dealing in looted art.