I recently found a possible entry for Ann in 1861 in Bethnal Green Workhouse
https://search.ancestry.co.uk/cgi-bi...1861&h=5664618
which gives a birthplace of Chiswick.
Chiswick registers are not on line - they are still held by the church and they offer a "look up" service for a donation..... and they have found a baptism for an Ann Mason in 1782 with a twin sister named Sarah (a Sarah Mason was a witness at the marriage of Ann Mason) to Samuel and Mary.
I am quite excited by this breakthrough, I just need to find something else to tie it together. I may be making more donations to St Nicholas, Chiswick!