Going Bonkers, can someone please help?

John Quay married Lucy Craine 18/10/1829

Sons Will, Manasseh and John appear on Census but not daughter Margaret born 1830, though she pops up as married to William Kewley on 1871 Census with Lucy living with them. Margaret is listed on the IGI List but I cant trace her anywhere else, how can I confirm she is my Margaret.

Thanks in anticipation

Mary