Any crossdresser who would withhold this information is setting the stage for disaster. Now, many crossdressers fear rejection and losing their woman if they do this. Also, it's better to know right away if she can't accept it. Also, not telling her creates serious long-term damage when she feels betrayed by your not having told her. Once you get intimate, a boundary has been crossed, and anything after that will be seen as betrayal.
Women fear betrayal perhaps more than men do.
But when a woman is just starting to know you, crossdressing will become one negative thing to examine against an otherwise blank canvas. But if she knows other things about you, your personality, your history, your likes and dislikes, she can get a more balanced picture. She can weigh this against the positive things she already knows about you. Now, there are some women who simply will not accept this. If you meet firm and unyielding resistence, you may have to consider cutting your losses and ending the relationship.