you might like to have a look at www.she-makes-the-rules.com. it's a great community of people involved and interested in female-led relationships, and there's a lot of good advice to be found there.
First of all, don't force the issue with her, it'll just make her feel more uncomfortable. because she hasn't been exposed to the idea before and will likely think its weird request from you. What can you do? Gently encourage her to read this guide. Once she sees just how many women are using male chastity devices as a way to enhance their relationships, she might change her mind. Explain to her that she has nothing to lose by giving it a try and ask if she would be willing to try employing the DreamLover system for a trial period (one month might be a good duration).
A recent article in the New York Times - stated that male chastity device sales have shot up dramatically over the last two years. In 2009, an estimated 20 million male chastity devices were sold. Clearly, the idea is really catching on with the modern woman.