I'd suggest telling her to make a list of things she wants to try; draw one randomly when you're a bit stuck, or use them as inspiration for your own ideas.

Also remember that with a small change anything can be D/S, just about. Housework is boring...housework in the nude chained to the furniture is pretty fun. A trip to the store is dull...a trip with a short skirt and no undies is exciting.

Some of the ball should also be in her court. Part of submission, in my opinion, is wanting to please one's top: talk to her and make sure she knows she can and should take the initiative on things as well -- initiative does not equate power! Meeting you at home naked, or emailing sexy photos of herself, or giving you a new whip for a present are very submissive. I have in the past told my slave to "think of something to please me and do it within 24 hours." Enjoy the squirming as she tries to find something suitable.

Best of luck and keep us posted!