Hi Kate,
The baptism and marriage records for Mapledurham have been extracted into the IGI.
James and Mary Lavel were not married in Mapledurham but became the first people with this name to appear in the Parish Register when Sarah was baptized. They went on to have a total of 13 children.
As there appears to be no prior connection between James and Mary to Mapledurham, it will be difficult to prove conclusively any particular couple is the couple. One thought is that, as they were new to Mapledurham, the entry in the Parish Register for Sarah's baptism might give their previous abode.
Best wishes
Colin