I know what you're going through all too well. What I did to help my parents warm up to the idea, was I took them to the local petland to see a variety of snakes. We visited a few times before my mom was ready to hold one. The best thing that I can recommend is exposing your mom to snakes. Even if you take her to the zoo, at least it's a start. It also might help if you were to compare a ball python to other snakes. My father was super happy I didn't get a corn snake after holding one. Maybe pester her about it for a few months