You wrote:
'Now my search continues since I only know that my G-Grandmother, Kate Gillis is from Frenchvale, Sydney.'
I have taken a quick peek through the book 'To The Hills Of Boisdale: Pioneer Families of Boisdale, Cape Breton and Surrounding Areas' (Fr. Allan J MacMillan - 1986) and I have failed to find Kate Gillis from Frenchvale. That doesn't mean that she wasn't there.
Your best bet is to contact Fr. Allan yourself as he has made a pretty good study of the area. He is currently stationed in St. Andrew Parish, Judique, Inverness County) but he can be reached at
liuichconc@ns.sympatico.ca.
Good luck