>Yesterday I did a late 6:00PM hive inspection and saw what appears to be 3 queen cells. The two that have been opened 1st appeared to be drone cells, I thought, but the third is definately 'peanuty' and as yet unopened. What should I do?
I wouldn't count on a queen unless you gave them some eggs. They will build a queen cell with drone eggs if there is nothing else around.
>Can a worker lay an egg that can become a queen?
Very unlikely but not unheard of. I would not pick that for an explanation.http://www.beesource.com/pov/lusby/bsmay1991.htm
I'd still give them a frame of eggs and see what develops. You may have laying workers now, though. Look for multiple eggs. You may also have a queen who just didn't start to lay until now. Is there any other brood or eggs?