Perhaps there's been a thread on this topic before, but if so, I wouldn't know how to find it. Well then,
Recently someone asked for the lyrics of a song with the words "jennifer, jenny, rosemary" in it.
To back up, I my reading about old ballads I've learned that if the plot of a ballad involved the supernatural (especially the Devil), then there was often a refrain between verses. This refrain would list the names of magical plants to protect the singer from harm by the supernatural beings.
An example is "parsley, sage, rosemary and thyme" as made famous by Simon and Garfunkle in "Scarborough Fair." For though these herbs seem like ordinary kitchen ingredients to us, to the old timers, they seemed magic. Rosemary, which has fascinating flavor and the name of the mother of God in it, was good in two ways at once.
In case you have never paid close attention to Scarborough Fair, the character doing most of the talking is the Devil.
As for the word "jennifer" in a refrain, it is a corruption of "gentian." Gentian flowers, with their incredibly brilliant blue color, were thought magical too. I know a song involving the Devil which has the refrain
Jennifer gentle and rosemarie The dove flies over the mulberry tree.