Legal Question in Real Estate Law in California

It completely depends on what your agreement was with her, if she is a tenant or a subtenant then you have to file an unlawful detainer action to evict, citing failure to pay rent as a reason. However, from the little facts you provided, it looks like the mother is a guest and you can pretty much ask her to leave. However, no matter what you do, since it is your roommate's mother, you should probably go over it with that roommate, as it could definitely create tensions in the house. By pleading with the roommate, you could avoid the awkwardness and have the roommate talk to the mother directly.

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I agree with the legal discussion in the previous answer. If the lady is a guest, she has no rights and can be told to leave. However, there are some facts pointing to a conclusion that she is indeed a subtenant and not a guest. First, apparently you are expecting payments toward expenses from her.....this sounds like rent. Guests can make voluntary contributions without becoming rent-paying tenants, but when it's obligatory, a court will tend to view the paying party as a (sub)tenant. Next, she has no other home. SOmeone with another address is likely to be deemed a guest, but having no other place points to being a tenant.