As a sissy maybe I can help with some ideas:
You could get her to wear a bra, panties and maybe something like a tank top or skirt under a large coat (if she has one) and go to the city or a very public place.
You could get her to buy some sissy clothes but get her to ask at least three memebers of staff for help/advise in buying things.
Depending on the weather and what you mean by semi-public, you could get her to wear her cutest and most feminie clothes and go for a walk around the block (at night)