Hey all- Just to complete the thread for anyone else havng this trouble. I still have no idea what may be killing the gals, but here is what I did:
-thoroughly scrubbed out the waterer with bleach water and rinsed well
-scraped every scrap of bedding out of the coop and hosed it down with detergent and orange essential oil. I would have preferred to use cedar oil which is very effective on bugs of all kinds but so many think cedar is harmful to chickens.
-Let the coop dry out, then mixed up a LARGE batch of Red LAke DE, wood ashes and a cup of boric acid. Put a heavy layer of this mix down on the coop floor, the roosts, and the part of the yard they dust in most.
-Waited until they went to bed, and powdered their butts with the DE/wood ash mixture. Oiled up all their legs too, as one gal's legs looked slightly lumpy- just in case of leg mites.
-Mixed up some oatmeal with a LOT of red pepper, garlic and an herbal worming blend. They loved it BTW
Crossing my fingers! Thank you all for your comments and advice, It is wonderful to have such an active forum to turn to for help and advice!