I went searching for "beautiful oyster girl" and found this. It's a story that could have inspired a ballad:

From Old and New Paris: Its History, Its People, and Its Places, Volume 2 by Henry Sutherland Edwards (London, etc.: Cassell and Company Limited, 1893), page 7:

In Paris a sempstress is supposed to be "gentille," a lingère, or getter-up of linen, "aimable," a flower-girl "pretty." The oyster-woman, although not characterised by any one particular quality, is credited with a combination of qualities in a more or less modified degree. Without being in her first youth, she is young; without being in the bloom of beauty, she does not lack personal charm; and frequently she invests even the opening of oysters with a grace which may well excite admiration. La belle écaillère is indeed the name traditionally applied to her. With the origin of this name a tragic story is associated.

There was once a charmingly pretty oyster-girl named Louise Leroux, known as La belle écaillère. She had a lover named Montreuil, a fireman, who, in a moment of frantic jealousy, plunged his sword into her breast. This horrible crime at once rendered "the beautiful oyster-girl" famous, not only in Paris, but throughout Europe; and in due time the legend of her life and love took dramatic form, and found its way to the stage. The interest excited in her unhappy end was all the greater inasmuch as her murderer had eluded justice by flying to England, where, in London, he set up as a fencing master. The Gaieté Theatre achieved, in 1837, one of its greatest successes by putting on the boards, under the title of La Belle Écaillère, the tragic history of Louise Leroux.

Since then the name has been familiarly applied without discrimination to the female oyster-sellers of Paris, many of whom have well deserved it.