I had a conversation with Mike Seeger about this issue. He was, by the way, an accomplished Jew's harp player. He said he had always called the instrument a Jew's harp and that he knew that the name was not perjorative. Nonetheless, he had taken to calling it a "trump" (which the OED asserts is still sometimes done in Scotland and norhtern England) because he had been fussed at at some festival for using "Jew's harp." I recommend his way of wriggling out of the problem: "Jaw's harp" is just plain stupid.