At last I have found the connection between Robert Henry Whitford, Ellen Daniels and Susan Garrett.
Susan Garrett 1775-1866 wasn't, as the 1851 census stated, the great aunt of R.H.W.but the great aunt of his first wife, Ellen Mae Brown. Ellen Daniels 1858-1846 was Ellen Mae Brown's grandma., and a sister to Susan Garrett. Their parents being John and Ellen Daniels.
One less outstanding query!!!