This appears to be another little gem served up by someone with, to quote from the title of a 1960s folk song, 'Plenty of Room up Top'!!
Whoever came up with 1761 as a birthdate for Joanna seems to have been quite happy with the fact that she would have been 40 when she married and then
49 when son John was born/baptised in 1809!! (I use age 48 as the cutoff point for childbirth and have only seen that on a couple of rare occasions!) And if we throw in son William Williams Glasson in 1814 then she would have been 53!!
So let's add to the information supplied by Karlan and see if we can bring some sensible thinking to the problem.
The son baptised at Ladock in 1805 is William Williams Glasson. Although the margin of the page in the image is very dark there is a small superscript 'm' that can be seen to the left of 'williams' thus indicating the abbreviated first name of 'Wm'.
Joanna's last child was son Thomas Richards baptised at Camborne in 1823. Thomas Richards of Treswithian Downs age 9 was buried at Camborne 3rd August 1833.
Now then, working on my 'cut-off' of age 48 for women to be having children this would then bring Joanna's prospective earliest birth year up to around 1775!
From the Tapley-Soper Transcript of Camborne parish registers:-
Samuel Richards, husbandman, and Joanna Glasson, widow, were married 15th December 1818 at Camborne - Witnesses: Cherry Jenkin and Jacob Jenkin
1841 CensusTreswithian Downs, Camborne
Wheal Camborne Mine
Samuel RICHARDS, 70, ag lab, born in County
Johanah RICHARDS, 60, born in County
Samuel RICHARDS, 20, copper miner, born in County
As the ages for adults were only required to be rounded down to the nearest 5 years we can calculate the approximate period when Joanna would probably have been born from her age in the 1841 Census. She was recorded as age 60 so, if she has been truthful, that would mean she was born sometime between 1776 and 1781! And you may notice that this corresponds perfectly with my note above suggesting the earliest she might have been born would be about 1775.
You may now have a slightly improved chance of finding a baptism for Joanna Williams.
Finally - I have found the following in FreeBMD which 'could' be the death of Joanna Williams:-
Redruth Registration District
March Qtr 1844
Volume 9 Page 171
Johanna RICHARDS
Redruth Registration District
September Qtr 1849
Volume 9 Page 210
Joanna RICHARDS
CT