Ask lots of questions on here & at a later date get your mum to read through your posts. Explain to her that Snakes don't need as much responsibility as a cat or dog (Smaller living area, feeding/cleaning once a week etc) & you are fit to look after one. I am sure when she see's that you are very keen & there is alot of us Herpers out there willing to help she will come around. Another way would be to get a fellow keeper to visit you both and take along one of their pythons. Have a hands on & talk a bit about husbandry, temprement etc & all should be good.