Hi Pat- This may be a long shot but then again maybe it's an important clue for you!
Dr. John H. Bush and his wife Mary Rowland were the parents of a Dr. Reuben Rowland Bush (1810-1874). Reuben married a Louisa Williams (1820-1874) on 9/13/1834 Caldwell Co., KY.
I do not know Louisa's parents nor any siblings. I do know that Dr. John H. Bush was in Laurens/Newberry Co., SC prior to coming to Caldwell/Christian/Livingston Co. KY between 1800-1810. To the best of my knowledge, he did not have any daughters named Mary/Polly.
There was at least one other Bush family in Caldwell Co at the time. They appear to be closely related to Dr. John H. Bush but I am NOT certain how.THis was William Bush and his wife, Mary Thetford. Mary Thetford Bush was the niece of a William Williams and his wife, Deborah Thetford.
Interesting, but this doesn't answer your question. It may point you in a direction, though.
If you could tell me the children of your Williams/Bush I might be able to help you more!