Hi Aistrop and welcome to RootsChat!

Marriage for Mary AISTROP here
http://tinyurl.com/y8msn7pMarriages Sep 1840
AISTROP Mary Thorne 23 545
WILLIMOT John Thorne 23 545
The marriage certificate would indicate if Mary had been previously married. Presumably, you have the name "John" from Mary Ann's marriage certificate - it's not unknown for people to make up a name. I can't find a burial for a John AISTROP around that time and place - of course Epworth was birthplace of the WESLEYs and Methodism was strong there, so John may not be in the C of E burial ground ... likewise, the marriage may have been Methodist, so more difficult to find.
I don't think there's anything to be gained by plucking any John AISTROP out of the IGI, especially the ones born after 1810 ... Mary Ann's mother seems to have been born back in the 1700s.
The National Burial Index has only one adult AISTROP buried at Epworth 1835-40 - a George on 23 July 1835 aged 27.