Note that the cenotaph spells her name, "Tiressa." I did not add that as a "suggestion" here, but am leaving it up to you. Since the only other source is a Gedcom, while at least with the headstone it is literally carved in stone, my guess is that she spelled it "Tiressa," at least more often than not.

Also, it says her actual burial was in Gilroy, Santa Clara County, CA. However, I could not find her there at Find a Grave.