These situations can get real tricky real fast. For a start, you should carefully examine the terms of her lease. Tenant's rights vary widely between various counties and cities. CA is currently under a temporary ban on evictions (for most circumstances) which is set to expire on July 1, but may be extended, either by the state or the municipality in which one lives. This includes the eviction of sub-tenants.
I don't know the regulations for San Diego, but they seem to be a little more landlord-friendly than other places, at first glance. Landlords have been affected by unpaid rent and some cities have recently passing ordinances tipping the scales to their advantage. It's a fluid situation and the poop is going to hit the fan in a few weeks.
Even when a primary tenant has a good relationship with their landlord, each may be relatively powerless to evict an unruly sub-tenant. The landlord may have no recourse other than to evict the lot.
Here are a couple of resources that may help:
https://www.sdcba.org/?pg=Landlord
https://www.sdhc.org/evictionban/
The second page lists a few phone numbers who may be able to provide better advice. I'm not a lawyer, just been dealing with a lot of this stuff. Good luck!