Good morning
Yes there is no reason for her to use the surname Williams when she married.
She quite clearly signs her name Agnes Williams and her father is given as John Williams not just John .
Her baptism does give her date of birth which matches with the 1939 index so it is her.
Just don't know what's going on.
But Good News the Family History Drop in when was cancelled because of the bad weather so I've got another week to have a go at it.
So I've made it through the Snow this morning ,Library is open and everything is go .
Now checked all the marriages for John Sellwood ,still got John Selwood to do.
Ciderdrinker