A Christmas guest : a novel / Anne Perry.

Enhanced descriptions from Syndetics:

Anne Perry has dazzled readers for decades with her gripping Victorian novels and has won new fans with her acclaimed World War I series. Perry's thrilling Christmas novels, recent additions to her unique repertoire, are set in the most joyous season of the year.

In A Christmas Guest, Mariah Ellison, better known as the vinegar-tongued Grandmama from the Charlotte and Thomas Pitt series, makes a stunning appearance in a bracing story full of devious delight . . . and certain death.
For Grandmama Ellison, Christmas is no reason to celebrate. And when her daughter and son-in-law plan a Christmas vacation to Paris sans hers truly, the cantankerous Grandmama is forced to stay elsewhere--and travels to the chilly, windswept Romney Marshes to spend the holiday with Charlotte Pitt's parents, Caroline and Joshua Fielding.

Grandmama is immediately miserable. For starters, Christmas with the Fieldings is nothing like the cultured life to which she's accustomed, and the Romney Marshes are unbearably provincial. When Joshua's cousin Maude Barrington arrives, Grandmama is at her wit's end. Although Maude is well traveled and friendly, Grandmama thinks she's improper and strange. But when Maude is found lifeless in bed, Grandmama senses foul play and takes it upon herself to assume the role of amateur detective--uncovering not only the truth about Maude Barrington but some startling truths about herself as well.

Enlivened with bold characters and vivid, witty writing, A Christmas Guest is yet another holiday novella with the perfect combination of mystery and murder mixed with a generous helping of yuletide cheer.