Hi Liz,
Brian wrote on his marriages introduction:
"Each page of a Register Book can record the details of two marriages. The Official Indices give only the volume name and page number so it is not always possible to completly identify a marriage and in this case all possible partners are shown".

So it doesn't mean a second marriage for her - just that two marriages are on that page, and without looking at the entry he didn't know which couple was which.
But you do know her marriage was to John Cain, so certainly worth a look.
The other couple on the same page must have been SKELLY, Frederick Ercy and CHRISTIAN, Mary Ann.

Sue