I was fishing in the dark when I posted on this forum but recent information has led me to believe that my Maria Cowles was indeed originally a Fulcher. Now given the size of Wymondham today (ie: not big... I know this as I was there just last week) it is entirely possible that your Mary and my Maria are related.
I have seen the physical evidence of Mary's marriage to Leonard in 1820 at the Norfolk Record office where I was this week. I think, most certainly that my Maria Cowles was originally Maria Fulcher but unfortunately I only got to see the Banns and not the full marriage certificate so I don't know who her parents were. *grr*
But she and John Cowles were certainly married there in December 1823. There were a good many Fulchers in and around Wymondham at this time. (I say AROUND because there are a lot of outlying areas where the farming families tended to move wherever and whenever there was work available.)
If you give me some time to collate the information I have, I will send it all to you directly. If you do not hear from me within a month feel free to e-mail me at the address given with this link as I work full time and sometimes get carried away with other stuff.
It would be interesting to find out if our families are connected.