Self defense is illegal in California. I hope she doesn’t get in trouble.
You do realize California has what’s known as a “castle doctrine” (California Penal Code Section 198.5), granting a justification for deadly force inside one’s residence. If someone forces his or her way into your home, and you have a “reasonable fear of imminent peril of death or great bodily injury,” then you would be justified in using deadly force to defend yourself. The California Criminal Jury Instructions (CALCRIM) do allow a jury to acquit someone based on a stand-your-ground defense. The instruction appears in CALCRIM #505 and #506.