Did a little more digging around on this. The interment record at St. Peter's doesn't have a date, but was made between 18 June and 29 October 1897. It does list the cause of death as diabetes, same as the Marion death record. I reviewed the death record and it also list her residence as Marion. I guess she must have moved there sometime after Joseph's death.
If anyone is interested I can post what info I have on her parents, grandparents and siblings to the Gaa mail list. Just let me know.