mechBgon

A Nova set to triple-plus-burst mode, perhaps? And how about a HID headlight, they have the combination of high output and long runtime that make for good daytime running lights. If you're not quite into the Nova thing, then Cateye LD1000's or Planet Bike SuperFlashes would be good, preferably out near the edges of the trike to show its width. These are daytime-visible. Make sure to aim them carefully so their hotspot is aiming right where the motorists will likely be.

Neon-lime outerwear like in Diane's avatar photo would also be worthwhile, and that's easily done with a $20-$30 ANSI Class II or Class III reflective vest. The reflectivity may not be much help from the rear but it'll show from the front & sides. I got one of this model in Lime (second pic below), and it's not quite like shown in the picture of the orange one, but the reflective material is some nice stuff and there's lots of it. Anyway, this is a lot cheaper than buying 5 neon-lime jerseys, and goes over whatever layering is needed for the day's temperatures. Whether you really need reflectivity or not, the color will help.

If she does end up riding in dusk/dawn/darkness, then go grab some DOT Conspicuity Tape from an auto-parts store, the red & silver stuff, and you can go to town with it. Rims, cranks, frame. And in darkness, you'll also want whatever stuff your state legally requires, e.g. reflectors.

edit: another idea is to get another vest and put it over the seat, if that can be done, so the rear of the trike's seat has a neon-lime cover with reflective tape. You can take it off and wash it as needed.