start slow, just hint at the idea that winter is awesome. Then hint to her that skiing could be amazing, with benefits not just for you but for her as well. do this for a little while to warm her up to it. Next is an important part, DON'T RUSH it, tease her a bit before you make the big move, you gotta have her ready for it. Work all around the idea of skiing, seriously carress the thought of skiing all around her, but don't go in too deep to the topic. When you and her just cant wait any more, then it all comes together....
"mom skiing is awesome heres a video of the hoodcrew this is what I want to do with my life"
she'll be quivering with relief when she says
"yes son, i approve"