Still trying to found out more about Lydia.
In the 1851/1861/1871 censuses she's living in Paddington and has Harwell as her place of birth.
The 1841 census for Paddington has not survived. She died in 1877, aged 74.
I have the birth certificate for her daughter Eliza Terry, born in 1838 in Paddington. Mother: Lydia Terry, formerly Dix.
She married Charles Terry in 1827 in Battersea, and was a spinster.
There's no Lydia Dix baptism in Harwell. >:

Any suggestions from you wise people?