Elizabeth Gaskell - how much imagination did she use?

I get the impression that Elizabeth Gaskell made very little up. Much of her stories seem to be based on her own observations. I read somewhere that some people were upset when they recognised themselves in Cranford. In chap 29 (I think) of Mary Barton, I just read a description of Liverpool shipping along the Mersey dockyards. That had to be an eyewitness account. I do not know if she wrote differently in her later books, but in Mary Barton, Gaskell is a very intrusive narrator. She keeps on stepping in an explaining or commenting on the situation. For example, in the Liverpool dockyard scene, she says that one of the sailors says something to Mary, that she, the author, would not be able to repeat (it being sailing jargon). In another chapter, Gaskell writes something to the effect that she could explain something better if she had the reference book to hand. Presumably, she was at her writing desk and couldn't be arsed to look it up.