Try looking at William Clover's nephews and brothers.
John Clover was in Arkansas around 1819-1830. His children may have been living with William. We know he had children according to the earliest Arkansas census records.
It would not have been uncommon in that era for uncles and cousins to raise your children. If John Clover was older than William especially.
Mary Clover could also be the first wives or sister to any of the following early Clover settlers Adam, Jacob, William, James, Isaac or John Clover. At around the same time 1810-1840 there was a George Clover living just inside the Okl/Ark line. The name of his wife and children are unknown.