Thing is, I'm doubtful they married when you are expecting them to have (if at all!)
Have you persued this route yet?
There is a marriage for Mary Topping in Wigton
Mar qtr 1839 vol 25 page 125
7 people listed
there is a groom missing off the list but I doubt if its William as I think he is still down in Essex in 1841. If you can match up the other 3 couples, then you might find out who was Mary's first husband and then look for the second marriage.
ps
*** from the above marriage search, you can discount Joseph Lowes, married Ann Robinson***