1/ You already approached her she said no, respect her wish.
2/ You turn 18 get a job, move out, get a place, get a snake.
Not everyone wants snakes in their house my parents never did and I survived, they probably actually did me a favor by saying no because when I left my house at 18 I started to travel and live in different countries (not something you do if you have animals especially snakes).
Years later when I finally settled down I bought one snake than 2 and now there are 2 snake rooms in my house and I breed several species of snakes.
Bottom line passion does not die, if you want a snake now, you will in 2,10 or even 20 years.
Snake require long commitment, enjoy the life of a 16 years old, then go to college, travel etc ......everything will fall into place when you finally settle down.