you could see if serc has any resources for that but whether you see a person cross dress,love the same sex,have funny colored hair, wear a turban or a burka or any other thing that is different then how your family is imo iyt is just a variation of how people live, no right or wrong way, just what each individual likes or wants to do, which as a society makes us great, if we were all the same life would be boring so while i do think you are doing a fantastic job enlightening your daughter on the difference you guys saw and her reaction i think i would explain it like you have been and make sure she knows no matter what kind of difference she encounters people should be treated with respect just as she would like people to treat her, sounds like she is a kind girl who is just learning about the world, hopefully the cashier understands and sees her apology