The OP said that her daughter's disability was "mild." I wouldn't assume the child was severely handicapped as you ascribed her to be.
If your daughter is disabled that way, she needs someone to be her buddy, to provide a buffer/spokesperson in this type of situation. Not everyone knows that disabilities don't always show on the outside.
While I don't see a need to advertise a disability constantly and to everyone, you need to provide support to help the child at times, not write them off with "some kids cannot learn to 'roll with the punches'" unless the disability is truly severe. Let them be more independent, paying for their lunch at the restaurant or checking out a book at the library on their own. Sooner or later, everyone would hope that their child would be able to handle their basic needs and make decisions, even if the library throws a curveball like new self-checkout machines. In that situation, going to a librarian and asking for help is much better than getting overwhelmed.
I've heard it both ways. I guess it depends on how interactive the candygiver wants to be, *shrugs*
I disagree - it's an opportunity for the shy ones to come out of their shell. No different than being rewarded with a sticker for an achievement at school. (Well, without the tooth decay, lol.) Just because it's different from your experience doesn't make it "beyond ridiculous." It's a fun way to interact on Halloween and as evidenced by the responses to this thread, it's not a unique idea.
FWIW, many places have "Trunk or Treat" in parking lots or cul-de-sacs to replace the house visits entirely. It's very popular in some places, unheard of in others. Different is just different, not wrong.
A little open-mindedness goes a long way. Doing a trick to get a treat is certainly much better than throwing eggs and toilet paper. The Tricks for Treats is far more positive in the long run and fosters communication as well as cooperation.