"She doesn't want it to happen any more than I do, we both know it's a threat to our relationship. So if anyone has an answer to this one, we'd be grateful."

I don't have an answer, but I was thinking about more or less the same conflict, in another thread. It sort of wandered into a different topic, but...

Another thought- don't create the situation where thir can inadvertently tug at your emotions. Maybe you need to restructure your dominance style with her, altogether?