Hi Peter,
Thank you so much for looking and finding that, yes it could be her as you say she was the only Martha born in the 1790's. I'll look into it.
Odd that she would have been christened after her siblings;
Ann 1787, Elizabeth 1785 died 1785, Joseph 1789, Elizabeth 1791, John 1793, Mary 1794 (my 3rd great grandmother).
All the best
Wendy