If your mom won't let you fully transition, perhaps she is willing to compromise. Ask her if you can stretch your relaxer for say 6 months or a year and see how it's going. After that time period, you can both re-access your hair and how your caring for it and whether or not you still want to continue not relaxing. If you do a good job of taking care of your hair and remain committed to being natural, perhaps over time your mom will see how important this is to you and jump on board.

Good luck with whatever you and your mom decide. And remember, in just a few years you will be able to transition and won't need her approval!
Last relaxer: September 2011
Follow my progress on my transition blog: http://naturallycurlyjourney.blogspot.com/