Hi Phil, not sure about "intrepid" but I'm doing my best "searching", altho not easy as I only have the same free websites as you to access, no more Ancestry etc for the time being.

Apologies for delay posting these findings but I've been going round in circles on this one for some while, far too many possible name & spelling variations (FreeBMD only finds hits spelt exactly as input, no near misses). Still cannot find Nellie or more likely Sarah Ellen/Sarah Helen in later Census, or in definite Marriage?Death records.

Similarly searching her father Thomas not easy as the 1851 Census c/o FamilySearch shows about four households including a young Thomas Gwilliams/Gwillim etc in the county, and all born abt the same time (b1850 wrt the 1881 Census I posted above), but not particularly Ashperton (East of Hereford, towards Ledbury) area. Widening the age filters on FamilySearch found this record which I think must be his family, thankfully Familysearch offers surname spelling varaints as here.

1851, Ashperton Road, Asperton, Ledbury, Herefds.

John Gwyllim Head M 51 Ashperton, Herefordshire
Phoebe Gwyllim Wife F 40 Munsley, Herefordshire
Ann Bruton Mother-In-Law F 75 Leominster, Herefordshire
Isaac Bruton Son-In-Law M 9 St Nicholas, Worcestershire
Thomas Gwyllim Son M 5 Ashperton, Herefordshire
John Gwyllim Son M 2 Ashperton, Herefordshire

So our Thomas was born abt 1845/1846, so I now think is his birth registration, ref FreeBMD;

Surname Given Name District Volume Page Transcribers
Births Mar 1845
GWILLIM Thomas Hereford XXVI 167 krisb
Gwillim Thomas Hereford &c XXVI 167 jammy-dodger

Which fits this Baptism c/o Familysearch;
Name Thomas Gwillim
Gender Male
Christening Date 25 Dec 1845
Christening Place ASHPERTON,HEREFORD,ENGLAND
Father's Name John Gwillim
Mother's Name Phoebe

also found;
Name John Gwillim
Gender Male
Christening Date 08 Oct 1848
Christening Place ASHPERTON,HEREFORD,ENGLAND
Father's Name John Gwillim
Mother's Name Phoebe

Name Milbrough Gwillim
Gender Female
Christening Date 08 Jan 1854
Christening Place ASHPERTON,HEREFORD,ENGLAND
Father's Name John Gwillim
Mother's Name Phoebe

Familysearch also gives this slightly "belated" marriage;

Name John Gwilliam
Spouse's Name Phoebe Bruton
Event Date 3 Aug 1845
Event Place Ashperton,Hereford,England

This MIGHT be our Thomas in 1861 Census, but seems too far from "our" area, north of Lemster);
Name Thomas Guilliams
County Worcestershire
Event Type Census
Event Date 1861
Sub-District 3 Bockleton
Parish Stoke Bliss
Registration District Tenbury
Gender Male
Age 15
Relationship to Head of Household Servant
Birthplace Herefordshire
Schedule Type Household

This is definitely our Thomas back home with his mother, now widowed I presume;

1871 Census, Mathon, Herefordshire, (Mathon is further east from Ashperton, towards Malvern/Worcester).

Phoeby Gwilliam Head F 59 Munsley, Herefordshire
Thomas Gwilliam Son M 25 Ashburton, Herefordshire
John Gwilliam Son M 22 Ashburton, Herefordshire

Looks like mother's death,FreeBMD, age fits her 1811 birth;
Surname First name(s) Age District Vol Page
Deaths Jun 1876 (>99%)
Gwillam Phoebe 64 Worcester 6c 155

I THINK this may be Thomas' Marriage to Hannah (Anna?), albeit maybe a bit late wrt Nellie's older siblings as per 1881 Census, needs proving of course;

Surname First name(s) District Vol Page
Marriages Dec 1875 (>99%)
Beavan William Hereford 6a 1076
Gale Hannah Hereford 6a 1076
GWILLIAM Thomas Hereford 6a 1076
HAMMONDS Alice Hereford 6a 1076

Also found these baptisms on "England Births and Christenings, 1538-1975," database, FamilySearch

Name Jane Elizabeth Gwillim
Gender Female
Christening Date 21 Jul 1878
Christening Place FOWNHOPE WITH FAWLEYE,HEREFORD,ENGLAND
Father's Name Thomas Gwillim
Mother's Name Hannah

Name Ada Selina Gwillim
Gender Female
Christening Date 21 Jul 1878
Christening Place FOWNHOPE WITH FAWLEYE,HEREFORD,ENGLAND
Father's Name Thomas Gwillim
Mother's Name Hannah

Again from Family Search;

1901 Census, Holme Lacy, Herefordshire,

Thomas Gwilliam Head M 56 Asperton, Herefordshire ("ordinary agricultural labourer")
Hannah Gwilliam Wife F 49 Woolhope, Herefordshire
Ado Gwilliam Daughter F 23 Fownhope, Herefordshire
Thomas Gwilliam Son M 17 Pencoyd, Herefordshire
Edith Gwilliam Daughter F 13 Weston Beggard, Herefordshire
Albert Gwilliam Grand Son M 2 Holme Lacey, Herefordshire

So our Nellie aka Sarah Ellen has definitely flown the nest by 1901, but where to ??.

I am the Hughes family on ancestry, my mum in law, was the grand daughter of Sarah Ellen Gwilliam, I have found her on four censuses 1881 1891 1901 and 1911. She did indeed marry Phillip Andrew Poole in 1906, he died as a result of falling downstairs in 1965, she died the following year in 1966. When she married Phillip she had two living children Dorothy Maud Milton born 1900 and Constance Milton born 1902. On the 1901 census she was shown as Sarah G Williams as housekeeper to an Edwin Arthur Milton at 230 Newtown Row Birmingham, Dorothy Maud was shown as his daughter.

He is shown as registered father on Constance’s birth certificate and was living at 230 Newtown Row Birmingham at the time of registration, mothers name shown as Sarah Helen Milton

Sarah Ellen Gwilliam also had 2 more children , one named as Cyril Milton Gwilliam who was born and died in 1899, no father shown on his birth certificate. The second one being Sidney Milton born 1904 and died 1906.

I can find no record of a marriage between Sarah Ellen and Edwin Arthur Milton, it is made more complicated by the fact that his first wife was also known as Ellen.

There is a record of Edwin Arthur Milton dying in 1934 leaving his estate to his widow Ellen, who died a year later and their daughter Ellen Elsie Milton was left in charge of the estate. The widow would not have been Sarah Ellen Gwilliam as she was now married to Phillip Andrew Poole.

On the marriage certificate between Sarah Ellen and Phillip Andrew Poole, Sarah was shown as Sarah Helen Gwillian, so I am presuming that she never actually married Edwin Arthur Milton, even though on 1911 census she showed that she had been married 12 years. I believe that they lived as man and wife and at some point around 1905/6 he returned to his original wife. My mum in law was led to believe that Sarah Ellen’s died of pneumonia

I would really appreciate if anyone has any further info as I am going round in circles!!