The cause of action is technically known as “vicarious liability”
Yes. Thank you. $PLC sued white supremacist Tom Metzger using it. A couple of skinheads murdered a black man. IIRC Metzger's connection was the skinheads admitted to being familiar with Metzger's hate speech from some telephone message site (this was 20+ years ago) that skin heads were invited to call. link to $PLC
Seems to me that if the teens were aware of Winfrey's comments that her stature is worth a 1000 phone calls of the type that convicted Metzger.