The Beds FHS marriage transcripts only go up to 1837, unfortunately.
However, looking at the other records, Mary Ann's parents appear to be James & Elizabeth. But that's the only baptism for a James & Elizabeth in Wrestlingworth. And I can't see any marriage for a James & Elizabeth in the Beds FHS surname index, even under variations of the name Dimmock. So I suspect Elizabeth and Lydia are probably one and the same, proving that is another matter though.
A few records which may be of interest...
Marriages - Wrestlingworth:
09 Feb 1829
James Dimmock; otp; single man
Lydia Cole; otp; spinster
witnesses: Mary Paterson, Thomas Waldeck
31 Jan 1830
John Dimock; otp; widower
Sarah Waring; otp; spinster
witnesses: Lydia Dimock, James Dimock
Baptisms - Wrestlingworth:
Parents: James & Elizabeth Dimmock:
17 Oct 1830: Marianne
Parents: James & Lydia Dimmock:
29 Mar 1835: Ruth
29 Mar 1835: Enoch
02 Jun 1839: William
09 Jul 1842: Emily
03 Feb 1850: George
Parents: James & Lydia Dymock:
16 Nov 1845: James
Burials - Wrestlingworth:
13 Aug 1850: Lydia Dimmock; age 37
09 Jun 1841: Ruth Dimmock; age 6
16 Apr 1852: George Dimmock; age 2
29 Apr 1833: Rebecca Dimmock; age 106
(I have no idea if Rebecca is related but thought she deserved a mention, given her impressive age)