Unfortunately, regardless of the occupant not having a lease and not paying rent, she is still considered a tenant.
California law requires a judicial eviction. You cannot lock her out without a court order. A landlord who acts to "simply change the locks" may be liable for both civil and criminal penalties.
The first step is to terminate the occupancy with the Three Day Statutory Notice. If she fails to vacate the premises after the required notice, you will need to file an unlawful detainer action to evict her.
The official Judicial Council Court forms can be downloaded from the California Courts Self Hep Center at: http://www.courtinfo.ca.gov/selfhelp/other/landten.htm
I hope that my information was helpful to you.
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