Mrs. Plansky’s Revenge by Spencer Quinn

Loretta Plansky is a tennis-playing retiree in Florida; she is comfortably off but misses her deceased husband. She has a demanding family: a 98 year-old-father whose unruly behavior in assisted living is about to cost her additional thousands per month, a daughter who wants money for a start-up (and her new fiancé), and a son who wants her to fund a dubious business venture. It is easier to say yes than to argue, also she's generous.