In many subsequent years you find them each listed separately with the same residential address. She is running a lodging house, as you see on the 1900 census if you scroll down. That's why she initially got listed as head, I guess.
EDIT:
https://www.ancestry.co.uk/search/ca...1900-1999_2599
The Elizabeth M. Farr at 928 Folsom is, I believe, the widow of William Farr. I think maybe those are other people entirely?
The 1906 earthquake must have knocked Elizabeth out of the business of lodging.