Oh no, so sorry to hear that about your new girl. I had "rescued" my Welsummer. She came with 5 other hens, they all had sticktight fleas on their head and face, poor girls. I was successful at treating them onsite prior to bringing them to my home.
All the fleas had died on contact with the Adam's flea & tick spray for cats n dogs, along with a nice slather of Vaseline and some Sevin dust equiv in the feathers and DE to the transport cage, shower curtain in the back of the SUV with DE spread around and the transport cage on that. Same at home, DE & Sevin dust equiv to ground and surrounding area that was aleast several yards away from main enclosure and where my flock roams. Also repeated the treatment for 2 more rounds while on quarantine, and I plucked off the dead fleas that were stuck on them and changed out the straw multiple times.
Happy to say they are all happy and healthy girls now. Molted and I believe some are now laying again.
That sounds like dedication in your part. Glad to hear that they are in good hands.