I'm getting a little confused. This appears to be the census entry for the Cooks in 1841
Tranchwood, Trevethin HO107/744/11 folio 54 pg 17
Christopher Cook 40 miner
Hannah 35
George 15
Harriet 11
Thomas 9
John 6
Mary 3
first 3 not born in county, the rest all born in county. Looks like they were married some time before 1841. Perhaps Hannah went home to her Mum for the birth of her first child - not uncommon. However, George was baptised in Trevethin 7/10/1827 son of Christopher(collier) and Hannah of Blaen y Cwm.
Hannah consistently gives her place of birth as Gloucestershire, Wesley aka Westerleigh until 1861. In 1871 she's Ann born Newport and Ann born Trevethin in 1881. Are you sure it's the same woman?
Possible death - Hannah Cook dec qtr 1862 Pontypool vol 11a pg 83
This might explain the change in age. If she was 35 on the 1841 census, she should have been born between 1802 and 1806. Her age at death in 1885 was 72.
Possible remarriage - Sept qtr 1865 Newport, Mon vol 11a pg 215 Christopher Cooke & Ann Morgan on same page.
To check Hannah's maiden name there are plenty of birth certificates to chose from
all Pontypool
Mary Cooke june qtr 1838 vol 26 pg 115
Sarah Cook sept qtr 1841 vol 26 pg 130
Benjamin Cooke june qtr 1845 vol 26 pg 135
(Benjamin and Joseph were twins according to 1861 census, but I can only see one registration)
William Cook sept qtr 1846 vol 26 pg 135
Amelia Cook sept qtr 1848 vol 26 pg 150
Agnes Cook mar qtr 1851 vol 26 pg 175
Martha Cook june qtr 1852 vol 11a pg 121 - she's the only other one I can find a baptism for - baptised 14/1/1853 born 19/4/1852.
modified to correct wrong death year for Hannah