Legal Question in Real Estate Law in California

First place, you should probably figure out whether this person fits the definition of a tenant or of a lodger. Generally, when a homeowner has a single paying roomer who may have his/her own bedroom but basically shares the rest of the house with the owner and the owner's family, the roomer is legally a "lodger" and not a "tenant," and hence does not have nearly as much protection against termination of the arrangement. There is no notice period and no need to go through a formal eviction process.

Second, it's been about ten years since I last researched the question as to whether disability entitles a tenant to any special treatment in terms of eviction processes. As I vaguely recall, courts have been somewhat reluctant to allow forfeiture of a lease for a short but cured default, such as late payment of rent, but otherwise there is no special treatment.

Phony lawsuits are a headache for which the best aspirin is good insurance coverage.

Your ZIP code suggests you may be in a rent-controlled area; I'd inquire locally if so; there could even be local ordinances giving non-tenant lodgers additional rights. You might also contact your county's adult welfare services agency to see whether they can give your roomer some relocation assistance.