Disclaimer: This is general information and not intended as legal advice.
In order for your mother to handle a claim on behalf of your father's estate, generally she has to be appointed the executor of his estate and be issued Letters Testamentary. You should consult with an attorney near your mother. If you are in the San Diego area, contact the San Diego Bar's Lawyer Referral Service (619) 231-858; if your mother is in North County, then contact the North County Bar's Lawyer Referral Service (760) 758-4755. They will give you the name of a qualified attorney to contact and you be able to get a free 1/2 hour consultation.