Rebecca was definitely old enough to have been the mother of any of the children listed with her on the 1850 census.
After doing this research for over 35 years, I can safely say, that the odds are over 90% that Rebecca was the mother of them.
Sometimes we have to take the leap of faith, and wonder, if after I have searched for so many years, what are the odds that someone else has more inforation than I do.Especially when we are talking that far back.
As far as records, your best hope is that Isaac left a Will.Otherwise there is very little information that is available.
The 1880 census states that Rebecca was the wife of Charles Coppage, and he was much older than she was.
It was not the normal thing for people to be able to afford cemetery markers made of lasting material.Most of the time, all the did was to put a wooden cross to mark a grave.Unless the people were rather wealthy, they could not afford to have the other ones.
Then too, much of the time, they were just buried on the family farm land.
Another thing, is that even if they could afford a marker, they were not made of granite, and they weathered away by the elements and were unreadable in latter years.