take her to the gym, dont make it an option, just sat, "this saturday you coming to the gym with me". if she asks why, tell her you think working out is sexy and you want to see her sweat. do the treadmill with her, walk, run, walk. if its her first time in the gym she dont want to be using all the different machines, just make it simple and fun.
then after the gym tell her she looks sexy as fukk and give her that good good. she's gonna be into it because after the gym her blood will be rushing and her libido will be up.
it is important that you make it a positive experience because otherwise she will see it as a grind and will dread going. and give her positive reinforcement by telling her she looks nice. make it something fun and enjoyable. after going a few times she will feel more comfortable going by herself. you just gotta get the ball rolling.