What do I do if I am being accused of a hit and run in another state that supposedly happened 9 months ago?

I live in Arizona and went to California 9 months ago for a baby shower and to visit my bro who is in the navy. I was there for 3 or 4 days driving from corona to the san diego area (where the incident supposedly occurred specifically Chula Vista). Now my mom got a letter in the mail saying that the car that is registered to her is involved in a hit and run (9 months ago!). The car is my sisters and I had borrowed it for that weekend. I have no recollection of hitting anybody while I was out there, and cant remember that far back to actually know where I was on the specific date the supposed hit and run occurred. What actions can I take to fight this? I don't know what to do. PLEASE HELP!