I don't know where you picked up this fil laitière thing because it makes no sense in French since it literally means 'thread dairymaid'. If you're looking for the origin of Filliter, you'll find it at
http://archive.org/stream/adictionaryengl00goog#page/n306/mode/2up. As for Fillaiter which is really Filliater, it's an Americanization of the French name Filliatre which comes from Old French fillastre 'son-in-law, stepson'.