So heres the thing...

ok thanks, anymore tips you can share?

I would explain the difference between Ball pythos and other pythons. Most people hear python and think some huge snake that wil eat small children(burmese, retics etcc...) Explain that BP's are very shy, they are not hunters but oppotunistic eaters, They are not agressive and will never eat anything larger than a small rat. Actually the reason they called Ball pythons(in the U.S.) is because they are so shy they ball up when intimidated. Educating people helps them appreciate these animals more. Most people lump all constrictors into one ugly category. I think one reason parents also hesitate getting their children pets is because when the pet looses it's novelty it becomes the parents headache. That is something you and Mom must work out no matter what pet it is. My kids got guinea pigs and rabbits and then got tired of taking care of them and then It became MY PROBLEM. So you have to realize this animal will live for 20+ years. Oh yeah no alergies to reptiles, thats a plus. Maybe you should start her of slow with a beardie and warm her up to reptiles. Also try getting her to go to a reptile show with you and she can hear first hand how these animals behave and what is needed to properly care for them. She will listen better to someone with experience than you who she probably thinks is trying to talk her into something. Good luck :)

I got a 15 gal. for my first baby, then movef her up to a 50gal abot 6 months later

BP's are great pets. Not too advanced, but they do keep you on your toes at times.
Very docile, very gentle.
What I do suggest, after you've proven to your mom, make sure you know 100% what you're getting into.
I work at a petstore and it bothers me so much when I have customers come back in returning their pets they purchased because it was "too fast" or "too mean"
People, pets are not clothing to try on and off and exchange when you want.
Especially a BP.
They live for a good 20-40 years in captivity with the proper care.
I've only had mine for about 2 weeks, but I took care of one that had a serious injury at the petstore I work at. It had gotten out and received a nasty belly wound when another employee tried to get him from behind the bird cages. I spent the next 2 months giving it anti-botics. Between that and the store manager helping me, giving me tips, I really grew fond of the big guy. (Enough about the python that got me completely hooked, Still miss him :(. )
Broke my heart when I had to sell it. Remember when I got it in on the shipment, was highly aggressive and bit me twice.
Anyways,
Just prove to her the snake will not be a burden on her or anyone else in the family. That it will be taken care of, and you're ready to accept the pretty big responsibility of taking care of such an excellent creature.
She shouldn't have a reasonable way to say no to a young man who is willing to dedicate his time to the care of BP.