Ask her to lend you that pretty little Halston you've had your eye on
She probably already knows
You never know
Somehow have a general discussion about the subject, saying that people must really want to do it, see how she responds
It's perfectly acceptable for a woman to wear men's clothes.
I guess it all depends on your relationship with your stepsister. Only you can decide if you are close enough. My stepsister first introduced me to dressing up in skirts as a game when I was quite young. 12 years later, there are only dresses, skirts and blouses in my closet.
Just be open and honest about this. I have come out to my aunt and friends that I do crossdress. They all accepted it and they now know the real me. She will love you still. There is nothing shameful or embarssing about being who you really are. Talk with her soon, because you need to do it and get it off your chest. If I can help you, let me know.
If you are honest just tell her how you feel when dressed. Tell her how long you have felt this way. If you are honest and reveal the truth most will accept it.
It was very difficult but I finally worked up the courage to tell my children I a transgender and prefer to live as a woman from now on, they took better than I even hoped for and they both support me
ill wash your dress in the morning sorry