I have looked at Amersham Baptisms for Catherine Toms and she is not there. As she puts out of County on the 1841 census and a check on the 1861 says she was born London, I am not surprised ( Should have checked that first) But there are several children to John and Mary Toms so looks like they are not her parents.
There is a burial for John Ainsworth 26/3/1834 in Amersham and logged at The meeting House - aged 67. So could be a relative.
When I was looking at the meeting house births, I recall that on some occassions they logged the parents of the mother. So I checked the birth of one of the children and Dorcas was the daughter of Sarah & David Beamsley .
Hope this helps
Jo