Make certain to read through all those papers in a probate file or an estate settlement. The widow may be listed under a new married name in later records, providing a clue to her marriage.
This can be a great help in states that do not have marriage records for the time period being researched.
Is great-grandpa’s will confusing? Are the relationships unclear? If so, make certain you have accessed all accountings of the estate that indicate what relatives received what amounts of money. If these records exist, the disbursements may mention relatives not listed elsewhere (people tend to “appear” when money is involve). These documents may also help to clarify relationships that may be ambigious in wills and other records.