I have a Margaret MANSELL b.1772 in Lilleshall parents being Samuel and Ann?that is all I have on Margaret, but I am not convinced that the Margaret you show as marrying in Westminster to a Patrick Delany is the same one. Also you say she died in 1866, there is a death registered for a Margaret MANSELL in the Jun Qtr 1866 in Oswestry which would have made her 94 at her death.
The 1861 Census shows a Margaret MANSELL, but have no idea if she is the same one, also she was staying with a Thomas Mansell born 1798. Not aware if she had a brother called Thomas.
1861 Census MANSELL, ThomasHead Mar M 63 1798 GardenerShrewsbury MANSELL, MaryWife Mar F 60 1801 Gardeners Wife Walsall MANSELL, RichardSonUnm M 19 1842 Printer Compositor Shrewsbury MANSELL, Margaret Lodg Unm F 88 1773 Formerly Shopwoman Shrewsbury Piece:1871 Folio:90 Page: 9 Address: Spring Meadow Cottage, Belle Vue, St Julians, Shrewsbury County: Shropshire