Thank you everyone who has helped with my research. I've taken all the suggested bits of information and I have put together a picture I believe to be correct - I am going to have to spend a fair amount of time looking into all of the new names and connections that have turned up to see if I can prove the suspected lineage.
Where I'm at with Charlotte Hellier:
Margaret Phillpott b 1827
Margaret Phillpott m. John Forward, 2nd quarter of 1846 - Abergavenny
1851 Census - Llanover Upper - shows Margaret Forward married and living with her parents - unknown at this time where husband John Forward is. HO107 2447 133 11
Margaret Forward (Phillpott) m. Job Hillier, 3rd quarter of 1853 - Abergavenny
Charlotte Hellier born in 1856.
1861 Census, Llanwenarth Ultra shows (from transcript) Margaret Ellin as wife, Job Ellin as husband - daughter Charlott Ellin age 5. This should be Margaret Phillpot, Job Hellier and daughter Charlotte Hellier. RG09 3995 51 1.
Margaret Hellier (Phillpott) m. Charles Escott, 2nd quarter of 1869 - Abergavenny
Margaret m. James Day in 1870. I haven't found this marriage yet but have solid info:
1871 Census, Llanwenarth Ultra shows Margaret Day b 1827 as wife and James Day b. 1839 as husband - there is a 1 year old Jane Day and four Hellier children listed as step son and daughters. RG10 5314 54 28
1871 Census, Upper Llanover shows Charlotte Elliott (Hellier) as grandaughter living with grandma Charlotte Phillpot. Not sure why Charlotte isn't with the other kids living with mom in Llanwenarth.
1881 Census, Llanwenarth Ultra shows Margaret Day (Phillpot) living with husband James Day, two day children and two Hellier children.
1891 Census, Lower Phillip Street, Llanover shows Margaret Escott (Phillpot) as mother in law with with her daughter Maria and Maria's husband Isaac Jenkins. RG12 4350 56 54.
This is what I've got done so far. Thanks again to everyone for the help - I went from stuck to a plethora of good info, now I am just going to vet the data.
I'd be happy for advice if anyone can tell me a good technique for tracking down complex ancestors (multiple surname changes from marriage or from different spelling / transcriptions). I normally look at census data but I have no idea how I would have tracked the mother without help because she would never show up on the census with a familiar surname.