Legal Question in Landlord & Tenant Law in California

If she is a mere guest, she has no right to stay at all. As soon as you tell her to leave she is a trespasser and you can ask the police or sherriff to remove her. Realistically, though, if you expect them to help you, you want to look like the reasonable person. So give her reasonable notice, but a firm deadline. Document it, and generally bend over backward to be reasonable and fair about moving her out. Then if push comes to shove and you have to get the authorities involved, they will be MUCH more receptive to helping you out. Your other option is to bring a legal proceeding up front, but there is no legal requirement that you do that in the situation you describe.