It’s ok, but I’m sorry to say that I don’t know the Mayfair Witch series very well, I read it a long time ago, and I read the “hybrid” novels where it crossed over into the VC verse… 

I don’t know of a blogger who focuses on that series who might be able to answer that for you, but there is the official Ricean Witch book about it:

The Witches’ Companion by Katherine Ramsland & Anne Rice

It was published in ‘96 though, and idk if there is an updated version which addresses the later books.

I would suggest that AR’s writing the witch series had something to do with:

• Witches can be considered another “othered” group, like vampires.
• …because Witches can be scary and they can be very frickin’ cool; what with the supernatural stuff they can do and the way they carry themselves.
• The fact that AR grew up in New Orleans – a place which has varying degrees of strong belief in voo doo and witches;
• AR grew up in a religious family; and she also addresses the rejection of witches in TVL and the horror of how innocent lives were lost as a result, so it’s not just about the witches but about how they coexist (or don’t) with society at large.
• AR also had the Taltos mixed in there, so like her vampire series, she was probably interested in writing stories that had not been told before.

Anyone is welcome to comment/reblog w/ ideas on this!