I'm sorry for your loss.
It does look like Lice/Louse in the photo.
You dipped the chickens, how cold is it?
I prefer dusting the birds with Permethrin dust so I can work the dust down through the feathers all the way to the skin. Dipping may not reach all the bugs and if the birds are in poor condition, getting them wet may weaken them more.
Put the dust in a sock and use it like a powder puff. Use your spray to treat housing, nesting boxes, roosting bars, etc. Repeat treating the birds and the housing in 5-7 day intervals.
I keep both dust and spray on hand.
How long have you had these pullets? I see you made a
thread on the 3rd. Was this when you got them?
I'd check crops to make sure they are emptying. Do provide grit (crushed granite) free choice.
These birds are on new ground and it's been at least 7 days(?) since you got them, so I'd also consider treating for Coccidiosis. You can find Corid at the feed store.
Liquid Corid dose is 2tsp or Powdered Corid Dose is 1 1/2tsp per gallon of water given for 5-7 days as the only source of drinking water.
Do not add any extra vitamins/electrolytes that contain B1(Thiamine) to food or water during the course of treatment.