When you are photographing the headstones of your ancestors be sure to look at the stones in the area. You may find missing married daughters or other family members buried nearby.
Many times when I find a couple and I know I have missing daughters or sisters, I look around for females with that first name whose age is somewhat near that of the person I am missing.
Once I find candidates I photograph the headstone, noting who she is buried with. When I get home I start looking to see if I can find a marriage record and/or other documentation to prove or disprove the theory.