In a Phrase . . .
. . . her justifiable anger devolves into a narcissism so extreme that she loses all sympathy.
She prescribes drugs for a potential addict. She bullies the addict's boyfriend. She divulges medical secrets, left and right. Etc., etc., etc.
She cares for no one's pain but her own. If her anger were directed at her husband, she might remain an object of sympathy. But she deals out blows left and right to anyone near her, with complete disregard for them.
Dr. Foster, in short, is a sociopath.