she's almost certainly not the progeny of William Bradford. Other records show he and first wife Dorothy May (who drowned a month after arriving on the Mayflower in 1620) had a single child -- a son.
Ezekial and Susanna Richardson arrived as husband and wife in John Winthrop's fleet of 1630. You can find their names on the manifest here: http://www.olivetreegenealogy.com/ships/neng_winthrop.shtml
It's still possible her maiden name was Bradford and that she is either a niece or some other relation to William (although some sources say Wm. Bradford's siblings all died in childhood).