Wow, now why on earth did I dismiss her, will have to look at that again. I'm sure I found an Elizabeth, same age, living with Doidge couple in a census and they were grandparents. I have an Elizabeth northey in the 1851 census living with the Richards and she is a niece, born Tavistock, date fits. Can't remember the first name, but male Richards is a witness to marr to George blake. I wondered if Elizabeth didn't live with her mother when she remarried. Must revisit this now as I'll not be content until I've solved it!! Thank you