Dear Diana Thanks again for replying to me! Mary Daffern is my Great Great Great Grandmother, her only child, daughter Mary Ann was my Great Great Grandmother. I imagine she only managed the one child because of her age at the time of her marriage. Her husband, John Mottram, my Greatx3 Grandfather left a will, leaving everything to Mary Ann's children, which I suspect means that his first daughter was either dead or childless when he died. I have recently discovered that Mary Daffern apparently embroidered a sampler at the age of 12 which is now on the wall of a distant relative, although I havent seen it myself.
I am a bit unsure about the 1806 baptism, unless of course she was baptised as a tiny baby, because her birth had to have been between May 1806 and April 1807 - but hey...if it is the only record that fits, then I shall be happy to claim it! I suppose that the best course of action would be to secure the marriage certificate as you initially suggested and hope that William is named as the father. I must say it is great to get going on this particular branch once again!
I really do thank you for working so hard on this for me.