Margaret (Jackson) McCoy was born around 1788 in Tennessee, and many online trees claim that her parents were Edward Blake Jackson and his first wife, Mary Hadden/Haddan. Margaret's profile here has no sources providing evidence that they were here parents, and Mary's profile lists six children in the biography, not one of them named Margaret.
Adding to the confusion, Daughters of the American Revolution's genealogy database does have a daughter Margaret, who married Jonathan Hall, and was the daughter of Edward and his second wife, Elizabeth Brake. While it isn't unheard of for half-siblings born in the 17 and 1800s to have the same name (especially when their father remarries), there isn't any evidence right now that Edward did have two daughters named Margaret.
I'm going to disconnect Margaret from Edward and Mary for now (and leave their names in the research notes), and if anyone has evidence, we can always reconnect them.