This is the way I probably would have handled it.
1) Get some paper work together, and present it to her all in one hit. ( stuff like maximum pyhton size, feeding schedule, enclosure sizes for adults and hatchlings, all the nitty gritty stuff )
2) discuss her concerns with her ( she may say " because I said so " and being a mother she has the right to, but there is probably more to it than that )
3) when you know the concerns, you can plan around it. ( eg.. escaping, enclosure size and what not )
4) try to compromise like others have said ( chores, school work )
5) If you get this far, don't rush out and buy the first one, try and introduce her to hatchlings and adults first ( this might help with future purchases )
6) If all else fails just "BEG" and play on the " Mother / Son " bond.
Good luck.