HI, My son has a ton of allergies, he is literally not able to eat anything unless I personally make it or watch it being made, while checking all ingredients. So, I understand your situation. This will be our second trick or treeting with him aware of the process. Last year I brought a bag of smartees, the one candy he can have. What I did was let him go to the door with his back, and when he got back I traded out his candy with a smartee. He was just 2 then, so wasnt really too aware. I dont know how this year will go. After the escond road of houses, my husband and I just decided to go home, since it was too hard. Like I said, I dont know what will happen this year.
Sorry to go off about my situation! Back to you, have you checked out FAAN? They always have ideas. My best recommendation is to take along candy your daughter can have and swap it out with the stuff she cant. Being allergic to nuts, I cant imagine there are too many treats that she'll get that she can have. The one thing I ran into last year was not bringing enough "safe treats", so at the end I didnt have any to give him. Thankfully he really didnt notice.
Good Luck! We sound like similar situations, Im just about 27 and stay home with my kids too. The allergies are always a battle, so if you ever want to talk let me know!