Apart from the 1861 census, what evidence do you have of where and when Annie was born? Did Ewings Groat have a maritime/naval connection? If so, perhaps Annie's father was similarly occupied and was based in Plymouth as she grew up, but that she was actually born elsewhere, and the family then moved to Portsmouth where she met Ewings. I can see no likely registration of her birth in Devon around the time you indicate. Have you found her in 1851?