The next step would be hunting down Mary Kreger's family members to see if any of them have the plant or photos. If her hybridizing garden was sold, maybe the new owners have some?
Check this out:
http://www.ahsregion4.org/page...
If you scroll down to the bottom of this page, you will see Mary Kreger listed under Rhode Island. See the note Watch Hill moved to North Carolina.
Here you go.... check out Charles Kreger's address and email under image information:
http://www.mydaylilies.com/day...
I'd email him!