Hi,
I'd start with the St. Joseph Church in Apple River,
www.rockforddiocese.org/parishinfo?parish=4. Yu might have to contact the Rockford Diocese.
Have you mentioned this to whoever you are purchasing her stone from? The local memorial marker company must have some kind of map to know where to place current burial stones.
If you're still looking for the answer, I'd contact the Galena-Jo Daviess County Historical Society,
www.galenahistory.org/. Successful Searching!