Lost this series years ago.
An uncle type character begins to blackmail his niece over text, causing her to send sexts and perform daring acts in public. The mother catches on, and gets looped into the blackmail. But, soon, the mother gets wise and the pair begin to openly and willingly perform for the uncle.
The first letter of the Author is possibly an E or F. Details remain slim. I think the mother reveals she knows while sitting at the kitchen table, the uncle type sitting across.
Thanks in advance.