There is this in the 1851 census
Upton Snodsbury
Sch no 49, Cousden Hall
George Pearce,head,W,50,Farmer of 250 acres,empl 8 labourers,Seven Stoke,WOR
Mary A Pearce,dau,u,23,Hanbury,WOR
Harriet Pearce,dau,u,22,Hanbury,WOR
George Pearce,son,u,19,Upton Snodsbury,WOR
Francis J Pearce,son,u,16,Upton Snodsbury,WOR
Thomas H Pearce,son,u,18,Upton Snodsbury,WOR
Caroline Roberts,servant,u,18,house servant,Throckmorton,WOR
The IGI has a marriage for George Pearce and Ann Hughes at Upton Snodsbury 6th Sept 1825. Seems likely to be this couple as the Thomas H in the above census is Thomas Hughes in the IGI, bapt 9th Sept 1832.
So it looks to me as though Harriet born Potters Bar 1821 is someone else entirely

Is she the one you want to trace?