I don't know the number, but "periodically" seems best. The problem with not talking about it is that neither of you know where the other stands. Maybe she does want to talk about i but can't get the words out or doesn't know how to ask things without hurting you? Maybe you need something like this, "Honey, I think you are not too keen about my cross dressing but it's real and it's part of me, and I think we need to talk about it. Would you prefer to talk with a counselor with me?"