My question involves a child custody case from the State of: California
Mother was granted full custody of an only child (no violence, etc.. connected to the granting of this custody) since then, the mother and biological father have married. The mother has recently found out that she has terminal cancer (2-4 years of life expectancy). The mother wants to be assured that their child will remain in the custody of her husband (child's biological father) upon her death or incapacitation due to her health issues. Does she need to file paperwork with the courts who initially awarded her full custody to request the existing custody be reconsidered as joint parental custody? Or...is it "assumed" to be joint parental custody upon their marriage and the prior singular custodial assignment was null and void? Is the other parent always (except of course in abuse cases, etc...) granted custodial rights since they are already the biological parent?
Thank you very much for your help in the matter.

