Co-signer of month to month rental contract and need to not be

[Bob Child]

Hi all.  My mom is the co-signer of a month-to-month rental contract in California.  My sister is living in the rental, but has refused to pay the rent.  My mom can't keep paying the rent each month for her and really wants to get out from under this whole thing.

Can she evict my sister?

If not, is my mom's only recourse to stop paying the rent and let the landlord evict my sister?