Margaret and her husband, George Butler, moved from Dublin to London about 1830. According to both the 1841 and 1851 censuses of England, Margaret, George and their family were living at 1 Francis Court in the parish of St. Paul, Covent Garden in Westminster. By the time of the 1861 census, they were living at 57 Greek St. (where their musical instrument business was located) in the parish of St. Anne in Westminster and at the time of Margaret's death in 1868 they were living at 29 Haymarket (again, the address of their business). Margaret died from "dropsy", an old term for the "swelling of soft tissues due to the accumulation of excess water, often due to congestive heart failure").
We know that Margaret was born in Dublin from the 1851 census of England, and we know her surname from the birth certificates of her twins, Margaret and Thomas. It's rather difficult to decipher the surname on the certificate but it's almost certainly Nead, a very unusual but not unknown name in Ireland. I have tried to locate copies of birth certificates for Margaret's other children who were born from 1937 onwards (civil registration of births began in July 1837) in order to verify her surname but none, apart from those of the twins (therefore both in the same handwriting), were found by the General Register Office for England and Wales.
Searches made to determine the Irish county or counties with the highest concentration of Nead families didn't reveal anything very useful but records were located for the following Nead individuals:
VRI (Vital Records Index):
Dominicus (Dominic) Nead, born 23 October 1816 in Boyle registration district, Co. Roscommon to Dominicus Nead and Brigida (Bridget) Brennan
Martinus (Martin) Knead (sic), born 13 November 1819 in Boyle registration district, Co. Roscommon to Dyonisius (Denis) Knead and Brigida Brenan (sic). Denis and Dominic above may have been the same person.
Patricius (Patrick) Nead, born 20 December 1825 in Boyle registration district, Co. Roscommon to Demetrius (usually Dermot or Jeremiah) Nead and Brigida Brennan. Dermot/Jeremiah and Denis and Dominic above may have been the same person.
Anne Neade (sic), born 31 March 1872 in Delvin registration district, Co. Westmeath to Thomas Neade and Jane Carroll
Mary Nead, born 10 July 1874 in Delvin registration district, Co. Westmeath to Thomas Nead and Jane Carroll
Elizabeth Nead married David Bruce on 18 January 1853 in St. Thomas parish, Dublin. David's father's name was also David and Elizabeth's was Patrick.
Griffith's Valuation (1847-1864): Michael Nead, occupier of land in the parish of Cloonygormican, Co. Mayo; Julia Nead, occupier in the parish of Killulagh in Co. Westmeath
Dublin City Census (1851): Pk. (Patrick?) Neade, 1 Hammond Lane in the parish of Michan's in Dublin; Jno. (John?), 17 Hammond Lane in St. Michan's
1841 Census of England: Mary Nead, Liverpool, born c.1791 Ireland; Michael, Croydon, born c.1821 Ireland
1851 Census of England: Catherine Nead, born c.1813 Co. Cork, married to English-born Thomas Nead; James Nead, born c.1824 Mayo and his wife, Elizabeth, born c.1811 Cork, living St. Pancras, London
1861 Census of England: No Irish-born Neads recorded
1871 Census of England: No Irish-born Neads recorded
1881 Census of England: Ann Nead, born c.1830 Ireland, married to English-born John Nead, living Wigan; Thomas Nead, born c.1824 Ireland; his wife, Eliza, born c.1819 Ireland; their son Michael, born St. Pancras, all living St. George, Bloomsbury; James Nead, born c.1857 Ireland, lodger in Cumberland; Thomas Nead, born c.1861 Ireland, lodger in Cumberland
1891 Census of England: Julia Nead, born c.1818 Co. Cork, living Shoreditch
1901 Census of England: Joseph Nead, born c.1864 Ireland and his wife, Mary, born c.1856, living Sale