I think Caroline is Thomas Wright's wife. Thomas (being older than Susan) was probably already married by 1841, so the witnesses to Susan's marriage - T. Wright and Caroline Wright would be her brother and s-i-l.
Thomas Wright 24 bachelor s/o William Wright gardener married Caroline Smith 28 widow d/o Francis Saunders at Walthamstow 18 November 1840. (transcript only - witnesses not included)
Caroline Wright in censuses gives her birthplace as Dunstable, Bedfordshire. There is a matching baptism of Caroline Saunders d/o Francis and Martha in 1812, and a marriage at Dunstable in 1831 of Caroline Saunders to Thomas Smith.
