Legal Question in Landlord & Tenant Law in California

Speak to the tenant and tell them why you do not want that person on the premises and ask that the tenant co-operate by telling her she is not allowed to visit ad you will have her arrested for trespass if she comes onto the property again as it is private property so access can legally be limited. Point out to the tenant that you need to provide for the peaceful enjoyment of their swelling to the other tenants and if he/she does not ban the person you will have no choice but to ask them to leave, using a three day notice if necessary.

If you don't want to get your tenant involved, you can also obtain a civil harassment restraining order against her. The tenant could join on that if he likes.