When Claire asks Jaime if the monks were from Germany he looks puzzled and she clarifies by saying 'Prussia'. While a unified German state did not exist until the late 19th century, the term 'Germany' was used to refer to the region in the English speaking world of the 18th century. Jaime would have understood where Claire was talking about.
The leaves suggested to be those of the Lily of the Valley only vaguely resemble the actual plant, and the place where they are found (a stone wall overgrown with vines) is not at all the typical growing place for this flower.