I don’t think that you will shock her. I remember reading a scholarly article where they had done research on the reactions of friends and family members who had came out as gay. This was in the early 80’s when “outing” was a thing. The research said that 95% of the friends and family were not at all surprised. Now they may not have been totally on board with that information but whose issue is that? Tell her and you will probably be having a good laugh about how nervous you were to approach her regarding the issue.
PS this does not mean I link crossdressing with being gay, but I think that it might illustrate the fact that we too often carry very heavy burdens when not disclosing. Actually, some suggest that undisclosed trauma is said to be worse than the actual trauma itself. (I find this difficult to believe in all instances) but there it is. Of course, you are also reading words by a girl so far back in the closet that I think I see Narnia.