DE does help to keep them at bay, but I would dust them well with Sevin first. Some folks use ivermectin, oil-based injectable but don't inject it. Put one drop between their shoulders and one just above their vent. It will keep lice and mites away...
I did use DE to kill lice on a rooster I bought years ago. It worked just fine. My flock has never had lice and didn't want them to get them, of course. I use DE in all nests and on occasion, dust the birds with it, but if I had more than a couple birds with lice, I think I'd go for the poultry dust or spray (pet stores carry lice/mite spray).
i checked three or four of them today and found one buff with them but didn't see them on the rest of the girls. i'll give the DE a try and give the coop and nests a good dose. thanks!