Hi Ann. We were all newbies once, so don’t worry. It is far better to ask questions and act, than ignore problems and hope they go away
It could be lice eggs which are usually laid in clusters on the base of feathers. They particularly go for the rear end around the vent, but are sometimes around the neck.
If she is at the end stage of moulting, it could be new feathers coming through. The head and neck are the last bits that grow them and the feathers come through with a white covering over them. These come off and make the hen quite ‘dusty’ for a while.
Don’t worry about dusting her head with DE. Get as much of her body as you can as lice are quite mobile over the hen’s body. If it is a really bad infestation, you can get stuff from the vet which is usually given to cats and dogs as flea treatment. I have heard people on here say they have been given a spray for under the wings. I also know people who have been told to use the spot on treatment — 1 drop on the back of the neck for a bantam, 3 for a full sized bird. If you go down this route, be aware the vet will usually advise you not to eat any eggs for a couple of weeks after treatment.