Jen is right in that there is no Boldon Union.
However, even though it does say Bolton Union I will check the South Shields and Sunderland Workhouses when I get a chance, just in case. I think the South Shields workhouse was not all that far away from Boldon.
If it was me after this look up I would be probably ask a RootsChatter in the Bolton area if they could do another look up of the admissions for that workhouse. Elizabeth may have entered at any point after she left the Tynemouth workhouse. I have had experience of others saying something is not there when it turns out to be otherwise. It does seem strange that Elizabeth is recorded as being transferred from Bolton Union but yet you, Sophie, have been told there is no record.
If I do not find her at the South Shields or Sunderland workhouse in the next few weeks I would definitely consider asking for a second check at Bolton. Hopefully, a RootsChatter in that area may be able to do it.
I have had a chance to check the Elswick Cemetery records and the newspapers today for Maria Battista death 1916. Nothing found. Of course she could have been buried elsewhere. I have looked at the burial you found which seems to be on FamilySearch. A look at their catalogue seems to suggest that this record was taken from one of 3 possible RC Church entries, the one at Stella, or St Andrew or St Mary both in Newcastle. If no one beats me to it in getting to the archives or the Mormon family history centre I will check this when I can.
The 1911 EC newspapers are missing at Newcastle library so I have not been able to check out the 1911 story in this newspaper. However, it may well be found in the Whitley Bay paper which I can check when at the North Shields library.
Could that be Pasqualino on freebmd who is recorded as having death registered in March quarter 1951?