I wouldn't be so worried about using the standard de-wormers like Ivermec and Safeguard. Have a fecal done to tell you what you need to de-worm. I have never used DE for deworming our pets but it is occasionally fed to them for pest control. It keeps the bugs out of our garden, barn, house, good stuff. We've dusted goats with lice with DE... I'm not sure if its in part due to the DE or my obsessive de-worming schedule but we haven't de-wormed any one in six months. All 10 horses just had fecals run and NO eggs were found.
Note: She says, "We make a big distinction between deworming and parasite control. Diatomaceous earth is not really a dewormer, but I consider it to be a form of parasite control. If the parasites get out of control, then you need a dewormer. I see people that throw the baby out with the bath water, saying they don't want to use toxic chemical wormers, so they quit deworming their horses altogether, and end up in trouble. It's important to make this distinction."