I'm so sorry to hear that hour Mom passed. My Grandma passed and it seems like I'm lost in paper work. She left her car to me so I went to the DMV with a Death Certificate and her will. They never looked at her will, just her Death Certificate an put her car in my name. You should do the same. Just bring an original of her Death Certificate and her registration. Again, I am so sorry for your loss.
Go to the DMV with all your info and her paperwork as well. It should be a fairly easy transition. It's crazy how much paperwork has to be done with everything. Hang in there. It will get better. So sorry
You will need to get a lawyer and let him help you out on this. In some states they do allow for a vehicle to be signed to another person without probate while in others you will need to start a probate.