Lilies That Fester

Description for LILIES THAT FESTER by Janis Harrison:

A DEADLY ARRANGEMENT
When Bretta Solomon -- recent widow, professional florist, and amateur sleuth -- is put in charge of an out-of-town florist convention, she knows that she will have to juggle many tasks while navigating the treacheries and petty jealousies of competing florists. Upon arriving, she soon discovers that the weekend will entail much more than rare chrysanthemums and dazzling bouquets.

A mysterious couple sends a letter to Bretta at her hotel, suggesting that their recently deceased daughter was the victim of murder, and then vanishes days later without a trace. Soon, a series of seemingly random accidents and mishaps begins to point to a more sinister plot against Bretta herself. In the space of a single weekend, Bretta will have to use all her wits as a detective and florist to discover what really happened before she's pushing up daisies...

This is #3 in A Gardening Mystery.