"Three Little Words," by Nancy Pickard, in Mystery Writers of America present Manhattan Mayhem, edited by Mary Higgins Clark, Quirk,2015.
Priscilla Windsor is a poor little rich girl. Not only does she come from a horrible wealthy family, but on the first page she discovers that she is about to die. "Death could only improve my life, she thought, and giggled wildly again."
Her long-time doctor, Sam Waterford, suggests she make a bucket list. Priscilla's has only one item: TELL THE TRUTH.
Three days later, she is murdered. Sam feels obliged to look into, not her death so much as her life. What he finds is disturbing, but does it include the motive for murder?
A lot of twists in here, including one I found unsatisfactory, but a very nice story anyway.