I'm inclined to agree with Jovi, and to hold out that "Y" is something to be avoided, or at least witheld (because that'll be one hell of a conversation, let me tell you) until a later date.
But sometimes its hard for someone to see a person in a different role than is expected, especially in relation to sexuality. See it from her point of view, she thinks one thing for many years, considering that to be right and normal. Then, without warning, you upset that view. I'd recommend just giving her time, to let her aclimate.