Adventures with 'other' instruments...
I found some information suggesting that the Epinette evolved from the Scheitholt in France about the same time the Fretted (or Mountain) Dulcimer was evolving in the US from similar sources. That would make it a cousin, rather than an ancestor.
There is an interesting discussion of the épinette des Vosges on the web page of a Musical Instrument Museum in Belgium.
There are additional references to FEUILLEE DOROTHEE VAL D'AJOL VOSGES on a French auction website
Jean Ritchie and her husband successfully tracked down a couple of the instruments in France about 1960.