Well, it makes sense that Latin "
Lucia" would be "
Lucie" in even the earliest forms of French. Since "
Lucie" is directly equivical to English "
Lucy," it comes down to the earliest record of "
Lucille" in either French or English, whichever you consider pertinent (Though comparing English "
Lucy" to French "
Lucille" may be peculiar).
http://www.prenoms.com/recherche/prenom.php/fiche/lucille