There's no such thing as common law marriage in CA. But CA courts do recognize "Marvin" claims, named after actor Lee Marvin, whose live-in sort of wife sued because he had given up her own acting career to act as Marvin's hostess, etc., and she claimed that he had agreed with her to treat her like a wife for property/support purposes, and that he held her out to others as his wife. The court ended up not finding for her, but did rule that 2 consenting adults who have a relationship not based solely on sex can make an agreement, like any other adults, to share property, provide support, etc. that the court would enforce.
So if your father had a recognizable "Marvin" agreement with this woman, she may have a claim to his property or to future support from his estate, or whatever they agreed to.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.