Prescot is the registration district - not necessarily the area in which the death took place
https://www.ukbmd.org.uk/reg/districts/prescot.html
The GRO index shows age 45 and the freebmd entry has been transcribed from that index. However - GRO online has age 35
https://www.gro.gov.uk/gro/content/certificates/Login.asp
Unfortunately - the death is not shown on LancashireBMD
I have accounted for the 2 likeliest St Helens entries - both are on the 1911 with their respective spouses.
There was a mental hospital in Rainhill - if Ellen was admitted (possibly after the birth of her last child) and died there - her death would be registered in the Prescot RD
Rainhill: That's a really interesting idea - value of local knowledge! - definitely possible answer to why Prescot death. I've ordered a death certificate for Ellen Birch hoping that might confirm addresses etc.
It feels very plausible as an explanation for why 'it' wasn't spoken about by grandmother. Not just a simple throwing off of Bolton roots but something more disruptive to the family and seen as a stigma at the time.
Sounds like people have found Rainhill records quite detailed - Merseyside Record Office, Liverpool, I gather.
Well, I think I have found my great great grandmother, Ellen Birch, nee Hart - but the Death Certificate is strange. But explains the different ages in transcripts.
It's at first glance for an Ellen 'Myers', died 10 November 1910, age '35', 'wife' of John Myers, widower, coal miner, of 79 Leach Lane, St Helens. Who was 'present at the death' at St Helen's Hospital.
BUT there's an official note (signed by Superintendent AF Mann, Registrar, 17 February 1911) which 'corrects' the information to 'Birch, otherwise Myers', 45 not 35, for John Myers read 'John Thomas Birch, core maker' and omit 'widower'. Info from Declarations made by John Thomas Birch (my great great grandfather) and Eli Roe (whoever he may have been).
So - genealogy experts - this looks as though my great great grandmother, mother of five children (youngest born 1904, family living in expected family unit in 1901), was living 'as wife' to coal miner, John. To whom she wasn't married, but the registrar at the time thought that she was.
Or is just some muddle over death certificates and paperwork.
NB: I've found one 1911 Census John Myers (then aged 41), coal miner, living with wife Alice and three children. There's another 1911 John Myers married to another Alice but he's a bricklayer. Not that I'm making any accusations.