A bit more digging has shown a marriage in Ilsington 1820 between John Parkins and Susan Leaman. Mary Ann's second daughter was called Susan.
The date fits for them to be Mary Ann's parents *insert hopeful icon
*pencils in Susan Leaman as Mary Ann's mum
I can't find baptism registers for Parkins/Perkins children
It would be nice to be have another reason to adopt Susan Leaman as mine.