Thanks to all of you for your help. I think that Brian may have hit the nail on the head. Frances (Slaughter) Heap must have been born in Alby.
I checked the IGI on familysearch.org for possible matches for the family listed in the 1841 census above. As one might have expected Samuel Slaughter/Slater and Willoughby Clarke had two sons named Samuel (presumably the first died young), who were christened in Ingworth, Norfolk: the first, Samuel Clark Slaughter, on 7 June 1799; and the second, Samuel Slaughter, on 5 October 1801. This could well be Frances (Slaughter) Heap's father, although he would have been a bit on the young side. In fact, I'd be more inclined to say that Frances's parents were likely Samuel Slaughter and Ann Peart, who married 20 April 1811, Aylsham.
However, it is interesting that the John and Ann Slaughter listed above in the 1841 census (who are apparently the son and daughter of Samuel and Willoughby (Clarke) Slaughter) also apparently had a daughter named Frances, who was born 8 June 1820 and christened 11 June 1820 in Alby (about the same time the Frances (Slaughter) Heap was probably born).
So, although the parentage of Frances (Slaughter) Heap appears to be a bit of a mystery, I think it's likely that she was born in Alby.
Thanks again for all your help!
Chad