Polishing cloth for harness hardware. I know the ADS ones are excellent, but maybe you can find some local ones with the short time to send for them. Flannel yellow fabric impregnated with something, really puts a shine on stuff, comes in a plastic bag. Velcro straps, bundle of 6 ea., 15" long for rolling up reins, traces, holding them together. Might call them cable ties. I get mine at Home Depot. Also good on electric cords, bundle of towels. I find the 15" ones excellent for many uses, while the shorter ones are just too short. These red ones "seem stickier" than velcro straps from other places or the cut your own size, off a roll of velcro.
A few years ago I bought a wrapping organizer by Rubbermaid, hangs up like a shoe holder. Piece of cloth back, with see-thru, heavy vinyl pockets that zip closed. That has been REALLY handy for holding many show needs, all visible and contained.
A self-assembled First Aid Kit for her trailer might be nice. I keep mine in one of the Rubbermaid tote boxes, with various items inside smaller boxes to keep them contained. The Gladware or Ziplock boxes are both inexpensive and pretty tough, to hold the items like adhesive tape, or the thermometer and scissors, some gauze rolls and so on. If the box gets tipped over, you still have all clean stuff inside the pile of smaller boxes. Some items I now carry are Super Glue for closing some big cuts and a cheap YELLOW Duck, digital thermometer (easy to spot fast) with the probe covers in a box. Sure a far cry from the old days! And with Christmas you might even find a RED tote, easy to spot among other packed things. You can put in things you KNOW will be needed for a lot less money than the pre-assembled First Aid kits they sell. Leave some boxes empty, she can then put her own "don't leave home without it" items in the kit.