Here's the answer to the ballad trivia question as provided from British Ballad from Maine- 1929:

Twice it is quoted in Beaumont and Fletcher's Knight of the Burning Pestle-act II, sc. 8; act III, sc. 5-and we are of the opinion that in addition to the two well-known snatches so often cited there is still another reference to it in the same play, in act IV, sc. 1. where the Citizen's Wife arranges a scene in the play for her favorite Ralph to act in:

"an let him be very weary, and come to the King of Cracovia's house, covered with black velvet; and there let the king's daughter stand in her window, all in beaten gold, combing her golden locks with a comb of ivory; and let her spy Ralph and fall in love with him."

The ivory comb, the golden locks, the maid in the window, all belong to the ballad of "Fair Margaret and Sweet William," already twice quoted in the same play.

Richie