The first verse that Ducky recites to the dead Marine's body is the rather gruesome conclusion to the English nursery rhyme "Oranges and Lemons". He continues with the infamous Lizzie Borden verse, and finishes with "Ring-a-Ring o' Roses" (aka " Ring Around the Rosies"), which is of uncertain origin but is commonly believed to be about the Plague.
In the first episode of Sapphire & Steel (1979), starring David McCallum, the ring a ring rose's nursery rhyme plays a key role in the plot. Wikipedia cites disputes of the rhyme's connection to the Black Death.
The character Daphne Ashbrook plays is eerily similar to a character she played in The O.C. (2003). There she played another drug-troubled mother who becomes estranged from her troubled son.
Amy Landecker played a counselor in Revenge (2011) similar to her role in this episode. She also had a motive that went against her practice.