These are the baptisms I can see to this family (all at St Leonards Shoreditch with parents George and Harriet), you probably have these already (can't see Harriet born c1829):
George William - born 28 March 1833, bap 21 April 1833
Sophia - born 2 April 1837, bap 23 April 1837 - died 1840
Mary Ann - bap 29 Jan 1840
Samuel - born 16 Apr 1842, bap 8 May 1842
Robert - born 29 Feb 1844, bap 24 March 1844
Sarah Elizabeth - born 15 March 1846, bap 12 April 1846
Nathaniel - born 25 March 1849, bap 15 April 1849
Emma Catherine - born 27 April 1851, bap 18 May 1851
Catharine - born 18 March 1854, bap 9 Apr 1854
Modified to add:
Another possibility in difference in maiden name could be that Harriet was born before her parents were married, or her mother may have remarried adding confusion? So she may have been born to a mother SELL (or PRITCHARD), but her mother later married to either of those names?
