Hi,
Prestbury seems to be on the "new" version of the Familysearch site. I searched on birthplace Cheshire 1760+/-10. There was no Jenny, but there was a Jane bapt at Prestbury 9 August 1767 parents John & Martha. This would seem a possible - there are several other baptisms at Prestbury for children with the same parents' names, so if you're able to place siblings with the family at any stage or they have a naming tradition these may help.
There are a few baptised as Jenny on that site, but not in Cheshire.
https://www.familysearch.org/The Cheshire Parish Register Project now covers Macclesfield St Michael which would be near (she may have been from Rainow at the time of the marriage, but not necessarily born there). However there doesn't seem to be a Jenny or similar on there:
http://www.csc.liv.ac.uk/~cprdb/