Hooooo boy. It's tough. Sorry she's upset. But I'd stop constantly going along with it. I realize you've worked things out with things you already have, which is great in the sense that she's learning to "make do" and to be creative and apply herself to a problem. Maybe she thinks you have an endless supply of materials and energy and ideas?
But the thing is, at this point, she's getting her way - she can change her mind a zillion times and you will drop everything and work with her. I think you probably should draw the line. If it helps her (and if you have the energy), set the 3 available costumes out. Hang them in the laundry room or set them out in an unused area like maybe the dining room table if you don't use that every day. Tell her those are her choices, or she is free to create something on her own from the dress up bin, or she is welcome to stay home with you and hand out candy to other trick-or-treaters. Then step away and let her get control of herself and the situation. Tell her she can make any choice as long as it doesn't involve making you work at the same task over and over, and as long as it doesn't involve screaming.
Maybe she learned some of this from her older brother, I don't know. Do they both do this a lot, or is it just around costumes/dressing in a certain way? If there are sensory issues with the feel of certain fabrics or materials, which some kids have, then I think you might have to switch gears. But otherwise I think you have to let her have a solo crying performance without you as audience.