Hey mlc,
Just an off the wall idea, but maybe you should pick up a hobby for which you need some alone time. Something like, say, playing an instrument. Or maybe you're more of a painter? Doesn't really matter what it is really, just as long as it is something that you have to do by yourself. The point is that it is
very easy to understand for her that you'll need a few minutes a day to practice your hobby. Or maybe you need a couple of hours on the weekends. Again, whatever works best for you, but I'd start small - minutes, maybe hours but not days.
You can use this hobby as a way to get her used to you taking alone time. And once she is used to, say, you taking fifteen minutes for guitar practice every day, then that half hour of meditation you crave for will go down easier as well.
Another benefit of the hobby: you can treat her to some music or a lovely portet of her every now and then. Chicks digg that!
Jim.